Improve the slope (7)
I believe the answer is:
upgrade
This clue is a double definition.
'improve' is the first definition.
(to upgrade is to improve or make better)
'the slope' is the second definition.
(upgrade is a kind of slope)
(Other definitions for upgrade that I've seen before include "Change to later model" , "Higher-standard version" , "'Improve, travel status perhaps (7)'" , "Improve equipment or promote" , "Bonus for plane passenger" .)