To reset your MPC to the default preferences, simply head to the preferences page from the main menu. This opens on the 'info' tab, with an option in the bottom right corner of the display to 'reset preferences'.
Once selected, a message will appear asking if you want to go ahead with the reset. Tap yes, and another message will appear, asking if you are happy for the MPC to restart. Once confirmed, the MPC will restart, and the preferences will be reset to the defaults.
Please ensure that the current project is saved, to avoid any data loss once the MPC restarts.