Upgrading Broadband package via website

[JRT23]

I'm looking at the “Special Offers” on MyBT and seriously considering an upgrade from Full Fibre 150 to Full Fibre 500. I have Digital Voice PAYG as well. With all all the fuss currently surrounding Digital Voice, I'm concerned that the upgrade would affect it in any way?  I would really not want to lose my number, it’s been around for a very long time and once gone it’s gone for good!  
I appreciate the change in BB will create a new 24 month contract, that’s ok, just the DV is a worry.

Any advice appreciated.

[licquorice]

Changing speed on full fibre is simply a matter of changing one artificial speed cap for another in software.

[ArtyVark]

Your number will not change.

Although I have been told when we switch from BT to EE we lose the number. Sales told me this when I've been trying to upgrade to Full Fibre and they offer me EE packages as well.

[JRT23 · Accepted solution]

Thanks guys, I'll go for the upgrade. I notice on the first order page there are three options, PAYG, Unlimited or Stay on Current. I hadn’t seen that before, I think that settles it. 
I'll post back when it’s all done. 

[JRT23]

Upgrade completed, no fuss or bother and with DV unchanged. I need not have worried, all is well and that includes a reduced monthly outgoing!  The only thing I can see is the new package is marked as “Cannot be renewed” which maybe a problem in the future but certainly for the next couple of years no issue at all. Many thanks to all who responded, most helpful.