Welcome to the forum.
This forum is searchable also as there're posts dealing with these issues.
Prior to changing them you might contemplate sanitizing your whole water system in a system prescribed manor.
With the pressure relieved you more than likely unscrew those canister filter housings.
Many times by hand, but a plastic filter wrench can often be required. You'll require replacement filters. Often they are of the 2.5" x 10" generic variate that can be found at a RV or home improvement store. Lubing the O-rings helps also.
Depending on the make and style of your water heater there could a sacrificial anode to be replaced. Flushing the water heater tank helps as it can present a rotten egg aroma in some instances.
Best of luck
J & J, DRV Suites ES-38RSSA #9679
GM Denali, 3500HD-Max, 4x CC, 8' DRW,
EZGo-TXT, Clubcar Precedent