any help on how to improve orange netgear wireless signal?

4 computers at home, 1 downstairs and 3 upstairs and for some reasons we get no or very slow signal upstairs so no internet.
i tried changing the router position, changed wireless channel but no luck.
what else could be interferring the wireless signal? one of my flatmate is a bit gothic and she has a 2 weird big mirrors in her bedroom,could that affect the wireless signal?
please help

can you put your router upstairs, any phone sockets up there.

As you are in a small flat it is likely you are surrounded by lots of other wireless networks and your channel is clashing with some of those.

Install MetaGeek's inSSIDer and look for a freer channel. Most users leave their router on the default channel set by their ISP. You might avoid these by choosing the extreme channels 1 or 13.

I'm surprised that you are having trouble with the signal strength of a Netgear router. I can see my Netgear DG834GT (or even the Orange supplied Siemens SE572) all round a large house. Hence I don't think it's the router itself, but more likely channel congestion.

Also maybe lots of steel rebar in the floor not helping with the transmission

i have got the Netgear DGN1000 from orange , i know that software you mentioned ,i tried it ,i changed it to channel 8 since no one around has it,i ll try for a while,and see how it goes,i reckon my flatmate's mirror affects the signal,as in her bedroom there is no internet what so ever