Relax in lift at college (7,2)
I believe the answer is:
lighten up
'relax' is the definition.
(I've seen this before)
'lift at college' is the wordplay.
'lift' becomes 'lighten' (I've seen this before).
'at college' becomes 'up'.
'lighten'+'up'='LIGHTEN UP'
'in' acts as a link.
(Other definitions for lighten up that I've seen before include "Plug in the fire" , "Unwind" , "Relax!" , "Chill" .)