As mentioned, you cannot change the signature added to the PDF. If you have added the signature using the Fill & Sign tool in Acrobat and saved the document once, it is not possible to change it.
If you are trying to change the signature already added under the Fill & Sign tool, please refer to the information in the following help document: https://adobe.ly/4hkf5Ym.
If you have added a digital Signature and locked the document, you cannot make the changes. If the document is not locked, you can right-click on the Digital signature and select Clear Signature.
p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.