Hi to everyone

Hopefully someone can help! I have a spreadsheet where users input a letter
from a to z into a textbox. How can I make Excel convert this letter to a
capital letter automatically, in case someone enters it as a lowercase
letter? Dont know if this can be done, but hoping it can!! I know about the
UPPER function, but that is not quite what I need as that function enters the
letter as uppercase into another textbox. I need it as uppercase in the
textbox in which it is entered.

Many thanks
Bigweed