So I've switched my old BT hub 4 to the new BT smart hub 2, yet my internet speeds are the same. Does the speed immediately change or do you have to wait?
There would be no change in speed unless you have changed your broadband package.
If you have changed from ADSL broadband to VDSL broadband (fibre), then you should get the new expected speed range right away.
welcome to the BT community forum where customers help customers and only BT employees are the forum mods
in order for the forum members to help please can you post the stats from your router HH6/SH2 then advanced settings then technical log information .
enter your phone number and post results remember to delete number https://www.broadbandchecker.btwholesale.com/#/ADSL
Someone may then be able to offer help/assistance/suggestions to your problem
the stats I asked for should show if adsl or vdsl
If you log in to the SH2 manager, click on Status and it will tell you the connection type.