With a 4.5 running a filter you'll need to change the water twice a week (about half the tank each time) for about a month. Once your tank cycles (this is when all the ammonia in the tank getting eaten up by filter baddies and put back into the water as nitrites so there is a reading of 0 ammonia on a test)>> http://www.bettafish.com/showthread.php?t=107771
This is a helpful guide on cycling.
After that is done, you can change the water once a week. Mine is a 5 gallon cycled tank. I have a nasty algae bloom which my nerites are too dumb and slow to keep in check so I need to scrub it twice. With a cycled tank you will never clean the entire tank 100% because the cycle will crash. You scrub the glass and decorations and always only add dechorinated water. All the bacteria you need is in the filter media so you should never clean this (or clean it all at once. I have to clean mine because I had too much planaria)
*I'm getting ahead of myself here
Your Ollie is a royal blue crowntail. And Flake is a red crowntail. (I think)