Existing Acts cannot be edited, precisely. Parliament will include the amendments in a new Act - usually these Acts contain both some new provisions and some amendments to old stuff. A typical formulation would be along the lines of "In the Blahdiblah Act of 2047, section 57, '...' shall be substituted with '...'. A good example that comes to mind is the Marriage (Same Sex Couples) Act 2013. If you use legislation.gov.uk, they add notes to older Acts pointing out any more recent amendments, but you do have to be a bit careful as they can't always keep up with the latest amendments.