How hard is it to install a new toilet?

It is not hard. On a scale of 1 to 10 of home improvement difficulty where 1 is painting a door and 10 is a tear-out down to studs and all wiring and plumbing, changing a toilet is a 2

https://www.lowes.com/projects/bed-and-bath/replace-a-toilet/project

Very easy job. Just make sure you have muscles to remove the old and set the new. Always use a wax ring or two to seal the commode to the floor. I am guessing you also have a shut off valve so there is no water problems. I am sure if you google or go to Pinterest you will find the process you need to follow. I have removed mine several times to install new flooring or remodeling projects.

It is fairly simple. Turn the water off and unhook water line. Hopefully you have a shutoff at the toilet. Then flush and scoop out all you can from the bowl. There are bolts on either side that will have to be removed. I suggest purchasing a new bolt kit. You will need to purchase a new wax seal and possibly the flange as well. Each time you move a commode the wax seal will have to be replaced. Lift the commode holding the bowl and pulling straight up. If you are doing this yourself, you can remove the top tank first to lighten the load. Clean old wax up remove old bolts and install new ones. Place new wax seal around opening. I like to replace old fixtures with the taller models. 17 to 19 inches. New commodes usually come put together and there are some you can buy as kits that have the tank innards. Again lifting by the bowl only, place new one over bolts. I would say this is heavy and you may want help. Snug up the new bolts and reattach water line. Check for leaks. Good luck.

It’s not that hard, IMHO the toilet is somewhat heavy or maybe awkward to lift and line up to settle on the precise spot on drain.

http://www.diynetwork.com/how-to/skills-and-know-how/plumbing/how-to-remove-and-replace-a-toilet

It isn’t really hard providing you have shut off valves and/or you shut the water off first! When purchasing your new unit ensure that the bolt holes will line up with your existing bolts, buy a new seal and you’re good to go...the rest is just strength to get the bolts undone and the old toilet out, new one in