Moves up since first of challenges is over (7)
I believe the answer is:
ascends
'moves up' is the definition.
('ascend' can be a synonym of 'move up')
'since first of challenges is over' is the wordplay.
'since' becomes 'as' (I've seen this in other clues).
'first of' says to take the initial letters.
'is over' becomes 'ends' (**).
The first letter of 'challenges' is 'c'.
'as'+'c'+'ends'='ASCENDS'
(Other definitions for ascends that I've seen before include "Climbs, mounts" , "Travels upwards" , "Moves upwards" , "Rises" .)