As to what is involved, assuming your exchange and cabinet are fibre-enabled then all you need to do is ring customer services and request an upgrade. BE WARNED, though: they will not automatically give you the best deal possible for your line, especially if you are on a Market 3 exchange.
My advice would be to do some research on what deals other providers are offering. PN will normally match any competitor deal but will not volunteer it in my experience. Customer support have a maximum they can go to but if you stick to your guns they will transfer you to the retentions team who are able to offer more.
By way of example I was offered a £2.49 discount on the normal £27.49 price of Unlimited Fibre Extra for being a long-standing customer. Retentions then reduced that further by another £2.50. However, when I told them that I was considering going to SKY as they had an offer for £10 for the first year and £20 thereafter, PN matched that by doing £15 for two years (which works out the same), a discount of £12.49 off the normal price. So it pays to go in forearmed!
I've also had a bit of an administrative nightmare making the change, so beware of the potential of having this messed up more than once. First my order didn't go through properly, then my engineer didn't show up (after ringing to confirm a few days before and being told everything was as scheduled. Then my expedited order was not followed up. Then I was put on the wrong product (i.e. not Extra) and told I had to wait until the original order went through and change after installation, otherwise I would have to start again. Then my modem wasn't sent out (I had the correct faceplate so went for a self-install). Then my discount was incorrectly applied for a year (instead of two).
In the end the installation went smoothly yesterday and all being well my upgrade to Extra should happen today. But I've had to spend in excess of four hours on the phone (including being on hold) to PN this last ten days just sorting out issues due to poor communication / follow up between PN and BT. It's a very decent price in the end, but it's certainly not always headache-free. Be prepared to learn patience and make sure you phone them regularly for an update. If I hadn't I've no doubt I'd still be waiting for mine.
