[NEED HELP] Help

I'm having a problem with the Xonotic settings. You can adjust the FPS in the "Misc" tab. The problem is that when I change it, the "Apply immediately" button still isn't clickable. What should I do? 

It should have adjusted the FPS setting without you needing to press apply, but to check you can press Shift+ESC to open the console, and type `cl_maxfps` and hit enter. That will tell you what it's currently set to. If you type `cl_maxfps` and then a number (like `cl_maxfps 150`) that will set it to whatever you type as the number (in this case, 150).

You can also type `showfps 1` to enable an FPS counter in the bottom corner of the screen

Most changes take effect immediately (eg when moving the slider or typing in the box), only a few need the "apply" button so it's only enabled when those ones are changed (if it gets enabled then you need to click it).