Are you using the Raspbian Jessie OS on your Pi? Need to change or set the resolution to better fit your screen or monitor?
Did you know you can now change or set the resolution on the Pi without editing the config.txt file manually? Yep! With the latest OS update, you can now change or set resolution directly through the desktop GUI.
Note: This is done pretty much the same way under the PIXEL desktop, but the menu just looks a little different.
Just click on the Menu button on the task bar, and click on Preferences. Then look for Raspberry Pi Configuration on the bottom of the list.
Then look about 3/4 way down the System tab section for, Set Resolution.
Click the down arrow and choose your setting, then click OK.
Then click OK at the bottom of the Config box and choose to reboot!
When it brings up your desktop, you should see the change! Simple as that!
If you don’t see these setting on your version of the desktop, you may need to do an update. Open a terminal and type: sudo apt-get update (If prompted during update install, choose yes to continue). Then reboot!