Quotehow do I uninstall SFML safely?By doing the opposite of how you installed it. I have no idea how you installed it. Perhaps you used apt-get and then you uninstall it with "apt-get remove sfml" or "apt-get remove sfml-dev" or something similar.
QuoteSo how do I do?The latest version of sfml depends on the xrandr library which is missing from your system (I guess sfml 2.1 didn't use xrandr yet).
I think you install it with "sudo apt-get install xrandr" but it has been a while since I have used ubuntu.