Crossword Genius

With business improving, increase living space? (5,2)

Ross

I believe the answer is:

trade up

I'm a little stuck... Click here to teach me more about this clue!

'increase living space?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'with business improving' is the wordplay.
'with' means one lot of letters go next to another.
'business' becomes 'trade' (trade is a kind of business**).
'improving' becomes 'up' ('up' can be a synonym of 'improving').
'trade' put next to 'up' is 'TRADE UP'.

Can you help me to learn more?

(Other definitions for trade up that I've seen before include "Buy larger house" , "Buy a bigger property" , "Buy a better model" , "Move to a larger property" .)

I've seen this clue in The Telegraph.
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