Amendment of a complaint restarts the clock for answering the complaint, based upon the date of service. Otherwise a plaintiff could sandbag a defendant with a huge, complicated amended complaint at the last moment before default. If a defendant has appeared you can serve by first class mail; if not, and I expect that they have not appeared based upon your questions about default, you need to have them personally served. My personal approach would be to serve additional copies of supporting documents - even when not necessary it helps avoid claims that "I didn't get them" or "I got confused" (even when pro se litigants aren't confused, some of them get lawyers who insist that everything about the case was incredibly confusing to them).

Although there are circumstances in which one might amend a complaint without filing an entire, new complaint to replace the original, this isn't the sort of case where such an approach would make sense, and it would likely both complicate the case for you and create confusion for the other party. I'm not sure where you're going with "do I just fill in the one box" - are you asking if your amended complaint should contain no information whatsoever except for the corrected address?