To have the 3G speed increased you will need to contact O2 data support team and ask them to make the amendment to your account the following is information about the 3G service from data support
"3G Speeds - 128k or 384k
By default a 3G sim with data but no voice will have a maximim of 384k data rate. By default a 3G sim with data + voice will have a maximum of 128k data rate.
Therefore a 3G data card for a laptop will come with a 384k sim. And Xda Exec for example, will come with a 128k speed sim"
The speed increase can be completed by changing the connection speed indicator on O2's systems this will need to be done by data support