Hi I've got broadband router provided by sky the best hub they have but the range wouldn't reach most parts of a 3 story 3 bedroom house.

i bought the ac1750 range extender 

the sky router is on the top floor and the extender is on the middle floor ( I have tried all sockets on the middle floor)

but the tv on the ground floor which is sky stream and uses internet often buffers.

what would my best solution be should it be to buy another one and that pass the signal onward to the ground floor? 
thanks