"Frozen" sliders are easy when people didn't lube them. Might have too much corrosion to remove slider w/o hydro pressing.
"Stuck" sliders could be corrosion or wrong lube. Wrong lube can swell the rubber "O-ring" bushings and cause pad problems. Most times you can fix this and use new "O-rings."
Normal operation sliders can stuck trying to move by hand
even enough and correct lube is used.
Should be fairly easy to remove using big pliers etc to press out the sleeve.
"O-rings" are the "Spring" for outer pads so won't drag the rotor.
Right after you lube them can slid easy but after a bit is hard to slid w/ hand pressure. Don't worry.
Sliders will move at brake pressure if you lube the correctly.Use Brake Grease.
If you think wrong lube was used then need new O-ring because swelling damage is permanent.
See my Cave, Brake Service
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)