Whilst a campaign is running, it can be paused and edited at any time. To pause a campaign, simply head over to your campaigns page and hit 'Pause':

Once a campaign has been paused, you can increase the budget but not decrease the budget. When you restart your campaign, it will re-enter the campaign list at the same position as when it was paused, therefore pausing / re-starting a campaign more than is necessary will reduce its visibility.

If you are a Pro Plan subscriber, you can edit your Custom Campaign Rules at any time - to do this, simply hit 'Edit'.