Take the bracket off, two bolts. Pull the rubber boot back and soak with penetrating fluid and keep upright so it doea not leak out. Put a wrench on the bolt and wiggle till it spins. Pull out with vise grips.
Works every time.
Sometime depending upon how badly it is seized you may need heat. I have used mapp gas or a hand held propane torch to heat the slider up while pulling with vise grips, of course after removing the caliper bracket from the hub. Consider replacing that slider if yoo use heat.
Next you will want to clean out the slider cavitity. A 1/4" dia meter bolt, chucked up into your drill, with a slot cut in the threaded end to receive a length of emery cloth will usually clean all the oocky out of there. Rinse with brake parts cleaner and compressed air and relube with synethic brake grease.