I get a blank screen when activating Vocal (themeforest) Theme

I recently purchased the Vocal theme.
When I try to activate it, I get a blank screen and my website stops working. I cannot even log into my wordpress admin panel.
Ive been told that “Vocal requires PHP 5.3+ and to make sure that server PHP version is min 5.3.” However i have no clue how to do this please help !