I have upgraded the seats in a Mk7 Fiesta with a set of ST seats from a Mk7.5.
Fairly simple to do but you do need to adjust the electrical plugs to make them fit.
00:00 Introduction
01:04 The Replacement seats
02:22 Removing Rear Seats
05:49 Fitting Rear Seats
08:44 Removing Front Seats
10:12 Modifying Electrical Plugs
13:00 Fitting Front Seats
13:40 The results
14:23 Recap