Catalina

Is it possible to uninstall or erase Catalina from my iMac. Ive been having trouble with the older system (not sure what it was, but my mac is 6 years old now. It wasn't being given updated or bug fixes so I saw a prompt one evening for downloading Catalina so I installed it. However its screwed up a lot of stuff on mimic, to the point where I cannot do spreadsheets, type out letters on Word etc. Ive since read that Catalina won't support 32 bit files so I cannot use the Catalina system. Can I remove it totally so I can go back to whatever I had before, or maybe another system like High Sierra which I see is recommended.