Change Screen Resolution on Raspberry Pi Desktop

I am using VNC headless, today I inadvertently changed my screen resolution and now everything is HUGE...I can't get to the edges of windows to click "Yes", "Apply" etc...how do I get the resolution back without being able now to click on anything outside of what I can view now?

text is too damn small. wake up !

Awesome thanks! This actually works :)

bruh add what you did in description. cant see shit on screen

Impossible to read any of the instructions you wrote

Got error can't open /media/vbox_GAs........

More easily!!! click on menu Pie - preferences - main menu editor, then the window will open, in left side choose preferences, click on rigth display settings, press ok. go back to the menu Pie - preferences - display settings. ;-).  
Why things can not be easier?????

Way to small to see the txt.

Hello, It is worked perfectly, but when I restart the system it reverts to the old resolution. Do I have to do this every system boot?