Firstly, minimise some of the open windows so that you are able to see an area of your desktop.
Using the right mouse button click on any area of clear desktop to open the submenu. From the submenu select the ‘Properties’ option (figure.1).
Selecting properties will open the 'Display Properties' window. The Display Properties will contain several tabs along the top of the window, select the ‘Settings’ tab, this should be the last tab to the right. (figure.2)
In the bottom right corner of the window the Screen resolution settings should be displayed. The number displayed shows your current screen resolution. The slider allows you to change your current settings. (circled - figure.2)
When you are finished with the Display Properties window note down your current screen resolution in order to select the correct Plan desktop wallpaper and close the window by clicking the ‘OK’ button.