My experiences doing this...I have the Navigator Professional lift away model. I use this in an area w/ a bunch of sewing thread on the floor. I try to get most of that up with a shop vac as the thread really does a number on the roller. After i removed the roller and cleaned it I gave the little black tabs on each end a spin and they seemed to spin easily enough but I figured I'd throw a few drops of sewing machine oil on each side. It went from spinning easily enough to giving it a spin with my finger and watching spin for about 30 seconds so a lot less friction. Hopefully the oil won't eat any of the plastic in there but as this vacuum is only about a week old I'll just return it if it does.

Also of note. When installing the little front roller wheels it is possible to push them in too far and they won't roll. I bottomed both mine out and then pried them back up just a smidge until they rolled freely.