I did it at the same time as replacing my hood - easiest bit tbh
You need some upholstery spray glue and a staple gun
Remove all remains of the old one work from the back forward >>> check the top corners of the new liner match up with the top corner of the rear bar where the rear window hinges from (i did this from the front and regretted it when i got to the back)
Put in a few staples to hold the rear and work forward glueing the tabs to the bars, when you get to the front make sure its tight and glue it down.
Check over and then finish up with the remaining staples and metal trim on the front