[Question moved to the Editing PDFs forum under Acrobat]
It depends what kind of text it is. If it's just regular text then you can use the Edit Text & Images tool (under Tools - Content Editing).
If the text is a part of an image then you can use that same tool, but you'll need to right-click the image and then select Edit Using, and then an image editor.
Editing the PDF will be painful at best. You should get the original file, which won't be a PDF, edit in the original app, and remake the PDF.