i agree with longboy- they stay on for 4 years. i would not bother getting them removed though as once they are spent it wont make a difference. if you really want them taken off you have to send the licence back to dvla (may have to pay for new one- i'm not sure)
You can get the relevant form (D1), to have the points removed from your licence, from most Post Office counters.
As Norman states, the fee is �19 for the postal service but if you choose to deal with the paperwork at the Post Office (or at a DVLA office), there's a �4 surcharge.