Yeah, peel it out gently Roy incase it's all dried out and brittle. Then give the glass and pillar a good clean with tar/glue remover or similar and make sure it's dry before applying the new one. It is quite a fiddly job, might be worth you getting a wallpaper scraper or duff credit card to help push the new seal upto the window so it sticks nice and solid.
Also, a hairdryer will help get the old one off and soften the new one up a bit, might make life easier.