Yes, you can remove a flea collar early, but we recommend using it for as long as it is effective. You should not remove it early to put a fresh one on that has full strength. The one you remove is most likely still effective.
Use your flea collar for as long as you can. You may also need to give your pet a small break in between collars. If you do this, be sure to do it during the fall and winter seasons when they are less susceptible to these pests.