patio door sliding glass door replaced in 2005 with low E Better Built sliding glass doors.

I need to identify the rollers need for the glass doors described above. I have two sliding doors in a three door track and would like to replace all four rollers. I have not removed the rollers yet and would like to have them in hand before I do. It appears the rollers are single wheel. Would there be a set of rollers I could order with a high level of confidence that they would fit correctly? Also, can these rollers be removed without detaching the lower door frame?