BuddyPress.org

Kristina unfortunately the upgrade from 1.1.* to 1.2.* is not straightforward you will need to read carefully the link that Andy provided and decide what parts of that apply to your situation i.e are you intending on trying to use the old theme and / or preserve older functionality in which case there are explicit steps you must follow with regards installing a backwards compatibility plugin. If you’re not worried about older features and are happy with accepting the new look and feel of 1.2 then you will probably need to ensure all buddypress plugins are deactivated (that may mean renaming them if not possible to deactivate from dashboard) then removing the old theme files as mentioned in the instructions then reactivate the new version of BP and test that things work with that alone before activating those plugins that are compatible with BP 1.2