I just installed Linux Ubuntu 20.04.1 LTS in a virtual machine. I want to change my theme and my icons style. I downloaded Unity tweak tool for that purposes. The tool is in /usr/share/applications/Unity-tweak-tool.desktop, but I can't run it. in fact I cannot run any .desktop file, and when I right click on a .desktop file and then go to permissions menu, I am not able to check the Execute: ''Allow executing file as a file'' field, it says ''You are not the owner, so you can't change these permissions''.
I want to log in as a root user(owner) and I tried typing sudo -i and sudo -s in the terminal and provided my password, but it didn't work.
How can I run .desktop files and is there a way to become an 'owner'??