Switching filters in a small tank.

Hello, I have a betta tank that is 2.5 gallons. This tank is about a half a year old and has been running a 10 gallon tetra HOB filter on it. In order to ease the betta on the rapid current that is caused by the large filter I've purchased a sponge filter that is much smaller. I'm curious how I can go about swapping the filters out since they are so different without crashing the tank. Any pointers?