Paint cans are airtight and store well for reuse or touch-ups, but they have a tendency to get stuck shut. This is because paint collects in the troughlike indent in the rim of the can. The lid is closed tightly, flush with this indent, and can become stuck if the paint dries between the two. While many people use flathead screwdriver or even coins and paint scrapers to open paint cans, they are not effective when the lid is stuck. Tools are made specifically for this purpose.
Position the paint can opener so the hooked end points upward toward the lid and stick it into the indent around the lid.
Press down on the handle to lift the lid. It may not lift completely off.
Rotate the can and repeat the same process about every inch around the lid.
Pour on a small amount of paint thinner, just enough to soak into where the lid is nested, if the lid has not lifted with the paint can opener. The opener likely loosened the grip between the lid and can, which will allow the paint thinner to dissolve the rest.
Pry the lid with the paint can opener again. This time, it should lift off easily.
Prevent the lid from being stuck again by peeling the paint away from the can rim and lid. Poke small drain holes into the bottom of the indent with a hammer and nail so that collected paint will drain into the can, rather than staying and becoming stuck under the lid.