Replacing seal on a folding shower door

[Sparklingbrook]

Shower door is the folding type so 4 short panes. I have found a stockist of the seal-sold in lengths-cut to fit. Apparently it slides in. what can possibly go wrong? Apart from the existing seal doesn't want to come out.....

Thanks TheDrugs, I did wonder about a bit of WD40 and the pliers. I am a bit concerned because if I balls it up then we won't be able to use the shower. It is supposed to slide out.