What version of Acrobat are you using? You can only do that kind of Editing in either Acrobat DC or Acrobat Pro DC.
Also, please keep in mind that "Editing" in Acrobat is not like editing in Word or InDesign (etc.), Acrobat is not a page creation application, Acrobat can only do small edits here or there. You can switch a image of the same size (as long as the PDF was not flattened) and you can fix a miss-spelling or typo, but wholesale alteration is beyond its capabiities and one needs to go to the application that created the original document and make adjustments there.