Step 1: Take old skimmer out.
Step 2: Put new skimmer in.
Step 3: Turn new skimmer on.
You might experience water/bubbles overflowing the collection cup at first, but it will break itself in and start pulling gunk out of your water column within a few days. My Reef Octopus had a half cup of skimmate within 24 hours. Good luck. Please post results!