Upgrading Mobilink Broadband Plan

I would like to upgrade my Mobilink broadband plan, but because its half way though the monthly time I pay my plan, will the new plan start from start of the new month or from the actual day I change my plan? I don't want to pay extra where I have already paid for the month plan and then pay more for another plan, so I would like clarification on this.

When I had a Mobilink broadband connection I remember that I had once upgraded to another tariff plan, but the time that I had changed my broadband plan it was the month end of my billing. To make sure that your money doesnt go to waste and that you have to call customer care to get any problems sorted out, just make it easy and change your plan before the start of the next months billing.