Connecting XFinity modem/router to linksys router?

Hi Folks,

Novice here. 

We have been using AT&T U-verse DSL.  We have cancelled AT&T and added Xfinity Internet to our Xfinity cable TV.  The Xfiinty modem/router is extremely weak, can't get internet in 3/4 of the house (never a problem with AT&T).

1.  What is the best solution?

2.  I have a Linksys 1900AC router.  Can this be used to improve internet thoughout the house?  If so, what are the steps?

TIA, 

Shane