Hi Aplayeru,
Many times difficult shifting is caused by the belt not fully releasing tension on the transmission pulley. Secondly, it can be caused by worn shifting forks inside the transmission caused by "forcing" the shifter or just simple wear.
My first try to correct the issue would be to purchase an OEM John Deere belt from a local or online dealer. The part number is M126012 which you can purchase
here from Amazon.
You should be able to find a local small engine repair shop that will install the belt for you. Be sure to bring your OEM belt to the shop with you to ensure they don't put an aftermarket belt on it. Figure on 1/2 to 1 hr labor. the deck needs to be removed and some machines require removal of other parts to get the belt on, others do not, and the job is fairly easy. Ask them to inspect and lube the shift linkage while changing the belt.
If that does not cure the issue, It is likely internal transmission wear and you will just have to live with it. Sometimes it helps if you make the shift while still moving slightly as you begin to depress the clutch. If you have difficulty shifting from neutral into first or reverse, try shifting into the opposite direction and move just a little then shift into the gear you want.
Hope this helps
Kevin