Fujitsu ScanSnap S1500M Operator's Manual page 440

8.
Remove the pick roller from its shaft.
Pull out the shaft as you lift the retaining clip.
Lifting the retaining clip with your fingernail may hurt or damage your fingernail.
Use a paper clip or something alike if you have trouble lifting it up.
9.
Attach a new pick roller on the shaft.
Insert the protrusion on the shaft into the slot.
Retaining clip
Shaft
Pick roller
Protrusion
Shaft
440
Replacing the Pick Roller
Pick roller