Hi Uroš,
That figure (50MB) simply reflects your current PHP configuration, so one approach here could be to adjust that value. Typically this is done by amending the php.ini file – though in some installations it is possible to change it with an amendment to your .htaccess file instead.
If you are unsure how to do this or which approach will work best in your environment I’d recommend chatting with your webhost.
Alternatively, you could leave that be and add an extra validation step which discards images that are too large (or chops them down to size) only when they have been posted through the frontend Community Events submission form – that way you could still upload larger files from within the admin environment.
I hope that gives you some ideas you can work with 🙂