Starter replacement

If a wrench won't work, use a socket. You can't do much without a basic set of wrenches and sockets. If the picture below, looks like what you have, the outside bolt shouldn't be a problem.

Are you working on it from underneath?

I can see most of the head of the outside bolt, and none of the inside bolt. The area is covered by the front engine mount. Should I remove the front engine mount? I feel like I just answered my own question.

Yes. Do I need to remove the engine mount?

Not according to my database. You don't remove engine motor mount. If a splash guard or air damn is in your way, you may need to remove it. Those stupid air-damns, where applicable, are a pain in the rear.

There is a flywheel access cover that you remove. Sometimes, there is like a 1/2 gap over the top of starter, some makes and models, where you can see the rear starter bolt, use a wrench, to get at it.