Replace the dome on a skylight by removing the retainer frame from the old dome, measuring the dome's exact dimensions, ordering a replacement, installing the replacement dome and reinstalling the retainer frame. Some skylight domes come with multiple inner and outer domes for energy efficiency. However, these domes install in much the same way as traditional models do.
In the case of multiple domes, first break the seal between the domes if you plan to only replace some of the domes. Break stubborn seals using a utility knife, but do not apply excessive force, as this can easily shatter the dome. If you are replacing all the domes, do not break the seals, and simply discard all of the attached domes together.
Running a bead of silicon caulk around the base of the inner dome prevents moisture from entering the structure. Make the bead about 1/4-inch in diameter, but leave 1 to 2 inches of space around each of the frame's corners. Prevent leaks between multiple domes by running close-cell double-sided tape between each dome.
When replacing the retainer frame, tighten the screws just enough to ensure that the assembly is firmly in place. Over-tightening the screws on the retainer frame can trap moisture in between the domes, causing an unpleasant appearance and potentially contributing to mold growth.