Here's the formulas to convert the data of the current textbox to UPPER case or lower case.
Convert To UPPER case
translate(., "abcdefghijklmnopqrstuvwyxz", "ABCDEFGHIJKLMNOPQRSTUVWYXZ")
Convert to lower case
translate(., "ABCDEFGHIJKLMNOPQRSTUVWYXZ", "abcdefghijklmnopqrstuvwyxz")
Convert first letter to UPPER case:
concat(substring(translate(., "abcdefghijklmnopqrstuvwxyz", "ABCDEFGHIJKLMNOPQRSTUVWXYZ"), 1, 1), substring(., 2, string-length(.) - 1))