How do i change my phones service provider details?

i changed my phone recently to o2 from orange. i got a prize that i can send free unlimited mms messages and it kept going to outbox. so, i went to the settings and it said that the only options for sending are orange internet, orange GPRS WAP or orange MMS. i have a nokia n95 please help asap cus its annoying me like hell! ill give best answer.How do i change my phones service provider details?
Hello.

You don't need to ring anyone.

Please go to http://getsettings.o2.co.uk/ServeSetting and follow the steps.

ThanksHow do i change my phones service provider details?
Best answer i can give mate is to ring up Orange costumer services, there the best that can help.