You didn't say year, but most after '97 are 7mm Allen key.
I needed a Hex 9MM worked great
Cavaliers from '94 to '03 all take 3/8 Allen key on calipers.
A 3/8 Allen key.
The calipers are held by 17 mm bolts.
Torx are almost never used on calipers. I think you will find a 7mm Allen key is needed for that year Mercury. Hard to see as it is covered by a rubber cup.
You need an oil change.
Use a 15 mm wrench to raise the tensioner below the Alt. with a clockwise motion
In that period most Cadillac calipers were held by 15mm bolts.
7mm Allen wrench
I think the calipers are attached with 14 mm bolts.
simple. get yourself a wrench set and an actuator tool to push in the rear pistons on the calipers.
All Cavaliers from '94 to '04 use a 3/8 Allen key on calipers.