Upgrade tariff

[Nikki10]

If I update my sim only plan does the extra data get added immediately 

[jonsie]

Upgrades normally happen within 24 hours

A change of tariff will be next billing date

[pgn]

If you are changing tariff because your data has run out, @Nikki10 - O2 offer one-off data bolt-ons to tide you over until your next month starts:

https://www.o2.co.uk/shop/all-tariffs/bolt-ons