That must be some website.
Just to elaborate...
The Web Panel has this to say about plan upgrades...
there will be no downtime for anything.
feature changes happen immediately.
your plan's billing start date changes to today.
any pre-payment left over is credited towards the new price.
there is a $49.95 one-time set up fee if you pick a monthly billing cycle.
Also, I am not sure what happens if you exceed your allocation before upgrading your plan. There is normally a $1 per GB excess charge, but this might not be the case if you upgrade before the end of the current billing cycle. If I were you, I would contact DreamHost support for exact details on this situation.
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