Can't tell if that is the rear or front roller,but you might have to take off the roll next too it to get it off.The track won't bag down enough those two places to give you enough clearence to get the roller out between the rail.

If you work a lot of rock you might want to get some rock guards.Not needed here,so a lot of the time you can find used ones cheap that people has taken off here.

As far a loosening the track after your relieve the tighter you can use the drawbar pin and put in the sprocket teeth and move the machine slow to pull the tighter and idle back.Good luck.