kiwirock: 2.4GHz and 5.8GHz are public spectrum for unlicensed devices. In a big city, it's just tough if it doesn't perform.
I think there's a flavour of Wi-Fi coming that uses something insane like 63GHz or something which is also unlicensed spectrum. But that's probably a mile away from ever happening on domestic stuff yet.
There are always things to improve wireless but it will cost a few more digits than a $110 router :)
If you have money to waste, you can Faraday cage your room if you wish.
Seeing that you are already squeezing 7Mbps, a more powerful radio may help. Most are only around 40-80mw. You can get some 1W plus units but that's another $130 bucks and won't improve the upstream but will help to drown out any other nearby Wi-Fi noise on similar channels (but not analogue devices and microwave ovens etc...).
Have you made sure your wireless devices aren't doing updates and downloads etc... too at the same time?
There's only so much half-duplex bandwidth available on an access point and the radio can only transmit in between interference as fast as the slowest connected client busy doing things (usually the furthest from the access point).
Change the channels, change the band, try a bigger RF output access point, if all else fails, wire it.
i dont really want to spend any money as in one year i am planning on getting fiber.However, in this year i cant just enjoy with such a low speed as i am a very heavy user.As i mentioned before everything is connected to the wi fi(not at the same time of course) and speed is very important.For examply my tv cant buffer the data and if connection is bad its just lagging.and i cant just pause it and wait till it downloads it.I tried to change bandidth to 20 but nothing has chaged...i only got ping twice as big