"Size" is to "resize" as "capacity" is to what?
I don't have the exact word you want, but "reallocate" might work depending on the context.
"Resize" is a verb and "size" can also be one, but "capacity" is never a verb.
If by "capacity" you mean ability and not volume, you have the verbs “capacitate” and “recapacitate”.
From The Free Dictionary by Farlex:
capacitate
- To render fit or make qualified; enable.
recapacitate
- To qualify again; to confer capacity on again.