upgrade wordpress

after upgrade wordpress system so far, i found some very in-actual activities:
1. wordpress added 4 users, i don’t know; included admin, administrator, pluginsuser. so i decided to delete all user and recreated mine.
2. plugin that i didn’t install.
3. plugin updated, in the manner i think it shouldnot

so now my wordpress has no plugin at all. so something will not be the same sorry for that now.