I think you mean your signature:
step 1: read this :
Signature Policy
step 2: click on
User CP near the top left corner of the screen
step 3: click on
Edit Signature- the first link on the left-hand side top; bar
step 4: Type your signature and then click preview signature at the bottom to sheck it to see if it's what you want, then click save signature if it is correct.
Hope this helps.