Can't update from v2.6.2789 via manual update
Are you 100% sure you are updating the right website/folder and not looking at the wrong one? Are you sure you are using the newest version of craft to install and not your old download?

If this is not the case. You could save your templates folder, All the folders you made yourself in the public folder and the plugins folder if you have any installed and make a backup of your current database and install a new fresh version of craft.

Then implement your saved files / database. Your database should be imported via the program or client you made your database in as this is not possible yet to do via the Craft admin panel. This is basically the same as a manual update.