I have a Snapper 30" cut riding mower. It cuts fine but when going uphill it will barely move, and if the hill is only slightly steep, it will not move at all. I have had it for several years and it just started doing that this past year.
Is there a simple solution to this problem?

Check the belt going to the transmission for proper tension. When the drive is engaged the belt should very very taut

This sounds like a fuel system problem provided you have a clean air filter and fuel filter.

Try with no air cleaner.
Try with the cap loose on the gas tank.

If these are not successful, then the problem may be fuel pump, if it has one or a carb problem. Namely a bad diaphram (assuming diaphram carb). I would suggest rebuilding the carb if the above fails.

How do I replace the drive belt on a murray riding mower.

I guess I need instructions, never changed this one.

SBlondee, your post is related a bit to the first person but you should always start your own post, click ASK. You will need to drop your mower deck as far as possible and remove the belt from the engine to the mower deck. Now you can get at the drive belt, it won't come off unless someone holds in the clutch and you can remove the tension from the spring loaded tensioner pulley.

Yep. Have you checked the clutch?