Mask without Case

Hello,

I've got the lower case password of a Hash. Now I want to Brute Force this hash, to get the case sensitive password. How can I do this?

Example:
lower case password: (known)            abcdefg
case sensitive password: (unknown)   aBcdeFg

How do I need to set the mask, to change the letters to brute force both upper and lower case?

Thanks,
Julian