Changing the case of the Nth character of a filename using Bash?

Changing the case of the Nth character of a filename using Bash?

I have a folder of files and I want to change the case of one of their characters at the 5th position.
From this:
ABC-xyz
DEF-xyz
GHI-xys
To this:
ABC-Xyz
DEF-Xyz
GHI-Xys
You'll notice the X has been converted to uppercase.
Any ideas how I'd do this in Bash?