can i exchange mac mini m2 to upgrade into m4

I would suggest to see if this apply (depending on country), it’s udually an online tool, that gives you immediately the trade-in value.

Then see what you could get by selling it yourself on the market.

In my case, i always ended up selling (or keeping for another use) as those trade-ins may not be so generous, above all if not within a year.

yes, it's the thing apple call trade in

you can read more about it here

Apple Trade In - Apple