The dashlet "My Activities" displays to old stuff: "about a day ago", although I've changed plenty of files since then… Though it is important for the team in order to see, who's working, which files have been updated etc.
what should we do now? how to make this thing updating?
The My Activities dashlet is specific to the Site Activities… and will be showing recent activities performed on the Site document library. The other activities will not be shown on this dashlet.