Replacing failed drives with higher capacity units

I have a Gspeed Q, 8TB, 4 disk drives 2 TB each. Can i use as a spare drive a higher capacity driver?
It is difficult and sometimes more expensive to find and buy a 2 TB unit instead of a 3 or 4 TB one. Incredible but true.

In order to maintain the RAID properly you should only ever use the same exact drives, not just matching capacity but same part #s so that everything aligns properly without issue.