Mum's ADSL WiFi connection really poor

[#1]

I've set this up using my Mum's JohnLewis/Plusnet details - she's been experiencing really poor WiFi in her home for months now. We've tried all the channels on her Sagemcom router and having spoken with Technical support on/around Easter we've recently received a new Sagemcom router but it's still exasperatingly slow. We've also tried both the usual (living room) and the upstairs sockets again to no avail. 

Firmware version - 7.275.11_F2704N_JOHN_LEWIS

I'm now using my laptop and an ethernet cable and there is no problem with the accessing the internet at this time. Any suggestions for improving WiFI as the only device my Mum has is an iPad? 

[#2]

Download a wifi analyse prog; check which channels are the MOST populated; then change router
to least populated channel.

I recall this is just a single band router, so you don't have option of using the less busy
5ghz frequency, which her pad may or not connect to ie the 2 frequencies.
Alternative is to buy an Openreach router off E Bay which can be reconfigured to PN settings,
and get a dual band one; these have better wifi performance.

[#3]

Thanks Gel, will work through your suggestions. 

[#4]

Moderators Note

This topic has been moved from ADSL Broadband to Tech Help as it's not a Plusnet connection and this isn't an official support forum for John Lewis.