Open Outlook
Click File
Click Options
Click Mail
Under Compose messages, click Signatures
Select the email account from the Select signature to edit dropdown (if needed)
Select the signature to update from the Select signature to edit dropdown
Edit the signature in the Edit signature box
Use the options to format the text (font, size, bold/italic, links, images)
To set defaults:
Under New messages, select the signature to use for new emails
Under Replies/forwards, select the signature to use for replies/forwards
Click OK to save changes