it would help if your posted results after entering phone number here https://www.btwholesale.com/includes/adsl/main.html
I have just gone down that route of upgrading to superfast fibre from the cabinet.
When the upgrade occurred my download speed when from 14mbps to just19mbps
BT tests showed likewise and an Engineer visited. Issue was wih the master socked.
Plugging direct into the master socked and got 40mbps. Engineer put an adaption onto the master socked which resolved the issue. Only downside was that I had to put the Router in the Master socket which is in a different room to my desktop and I had to use wireless connection instead of ethernet - but "hey-ho" it all worked perfectly after the adapted master socket was fitted and all my extension sockets were still live to use for telephones.
With new router will have to follow the instructions when fitting and will need to enter the new wireless password key into desktop and/or laptop . Password will be with the router - in my case it was on a little tag inserted in the side of the router and also a spare loose copy in the box.
Liked the new router. Can dim the lights and even switch them off and on at fixed times.
Admin password for router also supplied.