Hello
That gland is held in with a snap ring (round type). Loosen off the set screw then tap the gland into the cylinder until it bottoms. ( shouldn't be too hard to move) pick out the round snap ring with a screwdriver, ice pick etc. then you can pull out the piston, rod, gland assembly as a unit. remove both hoses first though so you are not working against hydraulic pressure.Be as clean as possible!!!
When you reassemble it leave the set screw loose until you have swung the boom both ways to seat the gland firmly against the snap ring.
Ed