Rollers are one of the more reasonable garage door jobs to consider doing yourself, with a real caveat. The bottom rollers on either side of the door sit close to the cable and the bottom bracket, and on a door with a torsion spring system, that bracket is under tension you cannot see just by looking at it. Swap a top or mid-track roller with the door down and it's a low-risk job with a ladder and a nut driver. Touch a bottom roller near the spring-loaded bracket without knowing what you're doing, and you're working next to the one part of the door that can put you in the hospital.
Our honest limit here: we don't talk anyone through the bottom-bracket rollers over the phone, and we won't send instructions for that step. If it's a top or center roller and you're comfortable on a ladder, that's a fair DIY call. If it's the bottom set, that's the one we tell people to leave alone and have someone drive out for.