Hi Lanette, it really depends on how you have your campaign set up. If people are currently in a wait step, then you'd need to run a smart campaign with a flow step of "Remove from Flow" which will stop people in that current flow, and then you will need to create a new smart campaign to send the email at the new time. Once people are in a wait step, that timeframe cannot be adjusted without stopping their flow.
If the setup is different, if you could please describe the setup we can provide other suggestions.