Make sure you are working with a table underneath your phone so it doesn’t accidentally fall on the floor.
The side without the buttons will be easier to take off since there is less bulk to work around.
If you don’t have long nails, try using a credit card instead.
The bottom corner is usually easier to pull off first, since it’s the furthest away from any of the side buttons.
You can also grab your phone and pull it out of the case if it’s being difficult.
If you had to put your phone case on in 2 pieces, it most likely has a seam on the sides.
You can find prying tools for phone cases at most tech supply stores.
Try not to force the tool down too hard, or you could break your case. Go slowly and gently all the way down. You may hear some slight popping or cracking as the case separates.
Think of your prying tool as a tiny crowbar to pry the pieces of your case apart.