How to case-INsensitive search/replace ?

[pstein]

I want to replace a string in filenames by another string.
For that I entered a search string.

How do I make this search string in-case-senstive ?

read: for "xxx" all the following filenames should be found:

aaxxxbbb.txt
aaXXxccc.txt
xXxddd.txt

[antp]

By unchecking the option "case sensitive"