Sounds like you're a rookie at this so I'll state Step #1.......

DISCONNECT THE BATTERY CABLES!!!!

Otherwise you'll find yourself learning arc welding as well as starter replacement. You WILL get high-amperage sparks going to places you didn't know were there.

The rest of it is pretty straightforward. Pull the wiring off the starter, pull the attaching bolts, and slide the starter out, either from the top or bottom. I find it easier from underneath but I have a hoist.

Dan