Donna, ours are on chains suspended from hooks. I just unhook, adjust, and replace the chain links on the hooks. Seedlings at end of February ( photo / image / picture from marlingardener's Garden ) This isn't a very clear picture, but the plastic shelving has holes drilled in it where the chain goes through, and the lights are suspended from two chains at each end.
OR....you can put something under the seed tray. I have a lot of paperback books so I use them to "shim" under the plants, so as to keep them a couple inches from the light. When they grow a little, I remove a book or two on each end. By the time all the books are gone it's time to prune or set them outside.
Yes, "S" hooks! Carolyn, thank you--I couldn't remember what they were called and I didn't think "squiggly hooks" was very descriptive.