New ultrafast router not giving strong enough signal for our home office needs

[Seastars]

We had a new ultrafast 165mbps system installed last Thursday to replace our existing sky superfast which was serving us perfectly fine. The engineer connected the new router in the living room above the Q box.  Previously it was in our hall attached via phone line which has now been taken away. The router in the hall served our needs well. Now we have breaking signal and essential online transfers for work are breaking up. We are way worse off than before the "upgrade" last Thursday. Because we need a signal to work. Any advice welcomed.  Many thanks indeed.

[Seastars]

Thanks for your reply, that's kind, but we have no way of moving the router or the expertise to check settings. Would appreciate any other guidance.