I have a sharp over the stove oven wanting to replace can't seem to find ways of removal

Most have a mounting plate behind them. With a few bolts that go up through the bottom of whatever is above it.

So, look in the cupboard (or space) above the microwave. There should be a couple bolts.
You will need to support the oven as you remove them so it doesn't crash down. Once out, it will tilt downward, then just lift it off the rack in the back.