Plumbing Idiot

What a great website, Thank you.
I am a plumbing idiot so take it easy!
The shower has 3 handles, need new handles on 2 so I bought a set at
Home Depot which has the handles and a square cap that you screw onto the
inserts with allen screws. The problem is there are things like "garages" that the inserts are inside of and no allen wrench is long and narrow enough to get in there. Can I get the "garages" off of the wall inorder to reach the screws? Thanks

handles

You may be lucky. If the allen wrench reached it you wouldn't have come here for advice. Take those handles back. They will ruin your stems and then you will need proper handles and new stems. Take one of the old handles or a stem to a good plumbing parts store, not Home Depot or similar, and get the correct handles thaf fit that faucet.