The first thing that you need to do is to locate the Rheem air handle unit. If you were there when it was being installed, then you will naturally have no problem locating it. However, if you living on rent in a house that had the air handler unit installed before you moved in, then you will have to do a bit of searching.
The cooling/heating system is typically fitted in the basement or some other lower- level room of the house. If you do not find it there, then search for it in the garage. Hopefully you will find it there.
Once you have successfully located the Rheem air handler unit, pull a flat-heat screw-driver out of your tool-box and use it to remove the screws that are holding the lower lid of the unit in place. If you are not used to holding tools, then ask someone else to help you out with it.
After you have loosened and removed the screws of the lid, remove it to gain access to the inside of the unit. Reach in to pull the filter out.
Clean the filter by washing it with soap and water. You can also vacuum the filter to clean it. If you go with the soap and water option to clean the filter, give it some time to dry before putting it back in. You can replace the filter immediately if you clean it using vacuum.
After you have cleaned the filter using either of the two aforementioned options, turn the filter in such a way that the side nodules point up and then gradually put it back where you pulled it out from, i.e. the lower opening of the air handling unit.
Secure the lower lid of Rheem air handling unit by replacing the bolts and tightening them with screw-driver.