I would like to know how to upgrade old doors without replacing

I have this same problem. I plan to strip off the top layer of the door then prime it. I bought some molding that I am going to add to the door like picture frames then paint. I have not completed it yet but I have seen this done online. Good luck!

Awesome something for me to think about thank you for your input.

You can go to a hardware store, lumber yard or a big box home improvement store, looking for Lauan plywood; this is what is likely the material you have currently. This material is thin, light weight and can be stained or painted. Use of a good wood glue and maybe small "pin" nails to hold it on to your frame. Then finish as you want , including using molding pieces if you wish.

I would go to Habitat for Humanity Restore with measurements. They usually have a ton of doors. I brought a nice solid mahogany door, new for $99. Hollow-core doors are a dime a dozen, most of the time you can get them free if you know any handymen or contractors, ask if they are replacing doors, ask Learn to Burn program at fire department if you can scavenge a house they are gonna burn.

Add a nice plywood veneer. You can get it in a variety of woods: oak, cherry, walnut or you can get a plain birch plywood to paint. Cover the door and back of the veneer with rubber cement then clamp and use heavy objects to hold down areas not covered with the clamps. .

Thank you it sounds like that is what we have I appreciate the advise