Open the Project Properties Window
To change the compiler and version being used by a project Project Properties Windows must be opened
Select the Compiler or new version to use
The list of all the currently installed compiler and language tools currently installed which are capable of building an image for the selected MCU are listed in the Compiler Toolchain box of the properties window. MPLABX allows multiple versions of the same compiler to be simultaneously installed. The version number of the complers are display in the parenthesis.
The currently selected compiler is always displayed in a blue box. To select another compiler or version simply click on the desired compiler.
Confirm the Selection
After you have selected the Hardware tool to use select "Apply" then "OK".