The 2-part algae attack posted by Ham Toast is a good way to go.
But you cannot do only half the job.
Take care of the problem that caused the algae, and physically remove the algae.
With the cause removed the remnants of algae will not be able to stage a come back.
The large and frequent water changes are an important part of the solution. Whatever went wrong, wherever the nutrients came from they need to be removed. Small, infrequent water changes are not going to put a dent in the accumulating nutrients.