...you really should remove, clean, and grease the top and bottom slider pins. It's not that hard, and you can do one at a time.

You don't give the year or brake type (which varies), so my advice here must be "generic", and is based on my experience with the 940 Girling ABS caliper.

Here is picture of the Girling slider pin kit from FCP:


Starting with either one, locate and remove the short bolt holding it in place.
The bolt may be either 12mm or 14mm hex head (in my experience).
Loosen the bolt by counter-holding the slider with a wrench on the larger hex portion.[my girling pins have a "square-section" rather than the hex]

With the bolt removed, you can pull the caliper back and (hopefully) remove the exposed slider pin and its rubber bellows boot, easing the boot off carefully.
Post back for tips on cleaning the bores and relubricating pins.

Chances are that at least one of the 2 sliders may be stuck or otherwise resist removal. If so, I suggest you start a new thread about that problem, which many here have overcome.

If you do decide to pull the caliper, the internal hex is 10mm.