Please perform the following steps:
- Choose Edit > Preferences (Windows) or Acrobat > Preferences (Macintosh).
- Signatures > Creation and Appearance > More, and in the Appearance panel, choose New or Edit.
My guess is your asking about the digital ID that you use to create a digital signature, and not the custom signature appearance that Aarzoo is referring to.
Once a digital ID is created it cannot be change, it is for all intents and purposes, cast in stone. The next question is from where did you get the digital ID? If you created one from within Acrobat you can delete it and create a new one, but if it came from a trusted third party certificate authority you need to go back to the CA and procure a new digital ID. Let me know which version of Acrobat or Reader you are using and I'll give your the steps to delete the digital ID and create a new one.
It is not clear what signature type you're using: Digital Signatures (based on a signing certificate aka Digital ID) or E-signatures which are just stamps of what you entered. I think you mean the latter, in which case the suggestions how to deal with digital signatures do not apply. How to delete an e-signature (a stamp) that you created and to sign again depends on how you created it and which Acrobat version you're using. Please, give us more info.