Deleted Theme Appearing in TwentyFourteen

Newbie here, apologies in advance.
Deleted a purchased theme from File Manager, ensured it was removed from WP, cleared my computer’s cache. Activated twentyfourteen theme, clicked ‘Customize’. Header is massive with menu items appearing from previously deleted theme. How do I restore WP to its original state, when first installed, and have all remnants of previously deleted theme gone? Would love a fresh, clean start. Any help would be much appreciated!