Open the front door of the printer to access the roller. Spread the black plastic retainers on each side of the roller away from the roller (Fig. A.), then rotate the top of the roller off of the shaft and lift to remove it. Note the orientation of the roller, and install the new one in the same way. However, the separation pad (see next step) should be replaced before installing the new roller.
Manually rotate the Tray 1 pickup roller shaft until the cams on the ends of the shaft are pointing up and rearward (Fig. B). This will give you a bit more room to work.
Now push the separation pad arm down as far as it will go and use a flat-blade screwdriver or pick to pry the old separation pad off of the arm. Do not remove the arm! It is extremely difficult to re-install the arm after it has been removed. To install the new pad, just press it down onto the arm. Make sure it is fully clipped in on both sides. Then rotate the pickup roller shaft back to its normal position (cams down) and install the new pickup roller.