Suspension and wheels are really something you need to read up on and have a detailed understanding of, before you go about modifying them. Definitely don’t do anything else until you read up on suspension and how it relates to plus sizing wheels, or you will just be taking another wild guess. We can help you, but it is apparent that need to do a bit of self-educating first. Spend some time Googling and searching this site.
But for now, tell us what size the current rims and tires are. Rim size should be stamped on the back so just take one of them off and take a look. Do you know your tire size?