Big job to make changes now :(
When you open your hive, you'll
be surprised at how far along they
are with comb building.
Just add supers from now on with
the size foundation you want.
If you order some quickly, there might
be an opportunity to replace a few frames
in your existing boxes before
the bees start drawing comb on them.
(these frames will usually be closest to the
sides of the box) They typically work these last.
You'll have an opportunity to change frames
that the bees have already drawn out, this fall.
You can use this "larger" comb for honey supers.
What type of frames and foundation
did you start with? If you have all medium
frames, changing can, and would be easier