Step 1: Take the portafilter out, then remove the diffuser screw and screen with a small flathead screwdriver.
Step 2: Use an awl or pick to gently remove the old gasket from the grouphead.
TIP: to gain leverage, insert the awl or pick into the outer edge of the old gasket using the grouphead cutouts.
Step 3: Install the new gasket (with the bevel side facing up). To fully seat the gasket in the channel, engage the portafilter until it stops (around 6 o’ clock or more depending on the age of the machine) then remove it again. Reinsert the diffuser screw and screen just past finger-tight, then you are done!