Hi, 

I have recently changed to a sim only plan but underestimated how much data I would need in a month. I went to purchase an add-on but then saw how simply upgrading my plan made more sense. How long does it take to change my allowances if I upgrade? Will it be instant or will I need to wait the 15 days until the current contract ends.

If so, would it make more sense for me to terminate my current contract and then buy another straight away, or would this not work because I would need a new sim card to activate it.

Thanks in advance,

Alex