How can I make over those hollow wooden doors?

WD 40 will help remove the stickers and glue.

The doors are paintable. Carefully sand the shine off, then prime and paint. I have heard you can skip the sanding and priming step with chalk paint but I have no experience with that type of paint. : )

You could also use molding to give the doors depth and characte.

I recommend Goo-Gone and chalk paint. It should only take a couple of coats, so one pint of a color should paint the sliding doors and the upper cabinet doors. If all of your walls are that light color, then you may learn to love the doors. They could be a focal point. If you have a child's room, you could paint the inner sliding door with a white primer and then a chalkboard paint, which comes in many colors now. The outer door would be great painted with the same or a coordinating color, then have a bulletin board or a cork board mounted on the door; and the board can be painted or covered in fabric or gift wrap. So many ideas! Best wishes 😇

I agree, paint and trim will update these so well. My parents home had this sort of door on all the closets. In early 1950s, it was a popular style because there was a shortage of building materials so they made do with what they could get. Dad put them in. Still work fine, better than hanging a curtain, but the varnished wood is a dead give away that these are very old door. The yellowish wood is just not attractive. People want a nice clean look, and paint is good way to get that look.

Adding trim is interesting idea too. The doors do look so flat and uninteresting.

Changing the hardware and the track may help too. The plastic parts that hold door in are probably old, yellowed, and tired too, so getting new parts will help them open and close smoothly and give them fresher look.

New knobs would help, but I wonder what kind of handle hardware the new barn door look uses? That seems to be a popular thing, having those sliding doors and they must use some sort of rustic or farmy type handle to open and close.

Depending on what color the rest of the trim is in each room, you want to keep consistent with that room, here are some picture ideas

just for something different or to spruce up tired old 50's era hollow doors (I have them in my house, too...) I painted the requisite primer stuff to cover the worst parts THEN GOT OUT THE FUN STUFF!! a natural sponge...no, not the kind to clean with but a beautiful sponge from the ocean...cut off little pieces and get little pots of your favorite colors and have a GRAND OL TIME dabbing splotches of different colors around the door frames...It's a hoot and a holler...and my tired old doors LOVED it so much that they look the best they ever have! I also drape my scarves etc along the tops of my doors and colorful caftans...makes my 1958 house sigh with relief...sigh...

I would buy some moulding and make a design on the outside.

Many years ago I wanted to make my hollow sliding closet doors look nicer but could not afford to replace. I took them down and removed the varnish or lacquer or whatever it was. I had plans to put on a wiping stain but the doors ended up a very pretty honey gold color so I did not need to do anything but use a light wiping finish. I did end up spending additional time doing the same thing to the casing and it looked great too - simply some elbow grease. Painting is not as easy as it sounds. In order to make the paint stick long-term, you will need to go through several steps - cleaning to make sure any oily residue is gone, possibly sanding, cleaning again, priming, then painting or you will have leak through of the old varnish or stain or the paint won't adhere well and will begin peeling.

This is what I did to my hollow door

http://www.hometalk.com/diy/windows-doors/doors/my-flat-closet-door-got-a-real-makeover-21919629

Love all the ideas. Thank you so much!!!!

All good ideas, just be careful if you are adding trim, since they are sliders. The trim has to clear the 2nd door.

Add trims, Paint, Wallpaper in panels, add mirror foil. Any will make a great difference.

Remove the stickers, with Goo Gone or peanut butter and paint the doors. You can add some trim to them to create a raised panel look if you like. It's an easy DIY.

First remove the stickers, anything oily will do it. Sand and paint or if you don't want paint an easily removable contact paper would look nice.

Hi Dani, use rubbing alcohol or goo gone to get the stickers off them and paint them and hang mirrors on the larger ones to make the room look bigger

https://abeautifulmess.com/how-to-refresh-hollow-core-doors/