First you have to take out the turtle(s). But be careful taking out a turtle can be a dangerous task. A turtle bite is painful and the don't let go. So try grabing the turtle from its side, and not put your fingers in front of the turtle.
Before going on put the turtle(s) in a container with atleast 18 ounces of water, in order to keep the turtle(s) hydrated. Next unplug the filter and take it out of the tank with any other decorative objects.