This is one of the easiest DIY tasks, and you probably wouldn’t have to remove the trim, but it may make life a little easier.
If you want to crack it yourself, and learn a little more about how you car is pieced together, the the trim tools are relatively cheap - I would recommend a set of levers and a pair of trim removal pliers. Always heat up the trim plastic before removing - the plastic can be brittle and snap if cold.
As an example, the type of tools are below (you can get cheaper ones, but I’ve used these for many years without any issues):
Silverline 927687 Trim Clip Removal Pliers 235 mm : Amazon.co.uk: DIY & Tools
www.amazon.co.uk
Workshop manuals are here:
Guide now located in the new
resources section of the site https://www.seatcupra.net/forums/
resources/leon-mk3-official-seat-workshop-manuals-link.24/
www.seatcupra.net
Look for one titled: General body repairs, interior. Then chapter 70 for sills, A pillar, B Pillar, C Pillar etc. It will describe the tool to use and location of clips: