Yes, you should disconnect the ring wire
if it is connected But - the reason for my italics - according to this:
http://www.kitz.co.uk/adsl/btsockets.htm#externalNTE , the ring wire isn't connected in the first place at the external box. Can anybody confirm if that's the case?
If the ring wire is not connected at the external box, and you don't have any internal master sockets, then disconnecting it from the remaining sockets will make very little - if any - difference toi the performance of your line.
Also, do try plugging a phone every socket in the house to confirm it works. Builders are famous for messing up phone wiring, and if any of the sockets don't work for a phone then the line will be hopelessly imbalanced which could mess up ADSL a treat. I'd also go a step further and unscrew every socket to make sure it's not a master Builders have been known to fit multiple masters by mistake, which does no real harm to the phones but, again, could mess up ADSL.
I still think you should post you stats before paying for help, though it's your choice. If we can see your stats we can at least advise you as to what kind of speed you should expect to achieve, even if we don't manage to help you achieve it. See
http://www.kitz.co.uk/adsl/frogstats.php- 7LM