Have you read this? https://codex.buddypress.org/theme-development/bp-template-pack-walkthrough-level-easy-2/
You now have six BuddyPress template folders transferred to your active WP theme folder in server which you should download to your computer to edit.
Open up the first file in activity/index.php file and make the following changes:
At the top of the file, replace:
`
`
with:
`
`
At the bottom of the activity/index.php file replace:
`
`
with
`
`
Save file and upload. Check alignment by going to http://yoursiteDomain.com/activity/. If all’s well, start making the changes on the remaining 12 files and upload to server within respective folders/subfolders.