Hi @Anonymous
Welcome to the forum.
😊You can change a Payg tariff once a month by going into your Myo2 ,which is located at the top of this forum.
Or by calling 4444 free from your mobile.
Or by contacting the Online Live Chat
http://www.o2.co.uk/contactusAny changes usually take place on your next anniversary date , although if you contact O2 on 4445 or use Live Chat they can override this and change it for you to start straightaway, although you will lose any allowances you have remaining in your current Big Bundle Tariff.
Alternative Payg Tariffs are here to look at
http://www.o2.co.uk/tariffs/payandgoHope that helps.
😄