Manage my usage

[#1]

I've just changed  manage my usage from £0.00 to £15.00.  I'm on the 10 GB  price
. Do I need to change it every month or will it stay at £15.  I am only doing this as my grandchildren are visiting and they  have all sorts of wi-fi equipment to use, like most kids these days. So I didn't want to go over the 10 GB .
I realize it would be cheaper if I needed this all the time to change my package but its only now and again I need to do this.
Hope this makes sense. Thanks.

[#2]

You should be able to switch from Value to Extra for a month at a time, and back again, so instead of paying up to £15 more for up to 15GB more usage, you just pay the difference between the two packages and get the full 60GB for a month.
Changes take effect on the next billing date, so you would need to ensure your grand-children's visits were timed accordingly...

[#3]

Thanks for your answer. I think that's a better idea.