In my Dashboard, My OSSN is 5.0, It tells me that there is a 5.1 update. But if I open my readme files, it tells me that I already have 5.1, and that is also what I downloaded 5.1 LTS.
Try to download latest build and follow the upgrade instructions. (v5.1 have latest build)
I allready did that
"Nothing to upgrade!"
Please follow ; https://www.opensource-socialnetwork.org/wiki/view/708/how-to-upgrade-ossn specially second last step.