The real problem is the line attenuation (62 dB downstream). That will limit you to ~ 2 Mbps. You might be able to improve the speed a bit by optimising your internal wiring, but it will only be a tiny improvement if any. I'm sorry to say that, as things stand at present, you're stuck with the low speed.
It depends how bad the internal wiring is, I managed to gain around 1Mbit by redoing the internal wiring in the house.
The dropwire ran to the dormer window upstairs, where there was a BT box. From there a wire ran through the wall to a junction box on the windowsill (inside) then there was a wire to the master socket on the skirting board, then it went through the wall into the next room, along the wall, through the wall again, down the skirting board of the staircase, along the bottom step, over the cupboard and down to the socket where the router was.
Further investigation revealed that the extension wiring between the master socket and the downstairs extension was damaged, and also that the wire between the box outside and the junction box on the windowsill was 2 core speaker cable, not twisted pair (courtesy of the builders that built the house). So what I had done was replace the whole lot with cat-5 ftp running a shorter route.
Now, 1 pair of the cat-5 carries the signal from the box outside. through the wall, through the (old) master socket backbox, along the wall, through the door, along the landing to the top of the stairs, through the floor into the cupboard, down the inside of the cupboard, into the (new) master socket, where the extension used to be. There the signal is filtered, and another pair is used to send the filtered signal up to what was the master socket and is now the extension, and half of the 3rd pair is used for the ring wire. This improvement resulted in a gain of 1-1.5Mbits of sync on ADSL.
