Get an appropriately sized phillips head screw driver and unscrew it. Unlike the bolts holding the track down, these are typically not through bolted.
The end stop has little ears that slide under the track, so it will take some wiggling to get it out and the new one in. Unfortunately it looks like Hunter did not leave you much wiggle room. You may have to shorten or remove the ears to make the job easier.
Put some sealant, I use butyl tape for this, wiggle the end stop back in and put the screw back in. Sit back and have a

you've done enough work for the day.
