Campaigns that have been submitted and paid for can be edited from the Campaigns page.
Select the campaign you'd like to edit from your "Campaigns" dashboard.
Once campaign has loaded you can either select copy or edit in the top right. (Copy will create another campaign that is exactly the same as the selected campaign, which is great for doing A/B testing)
After clicking "Edit" you will be taken back into the campaign builder where you will be able to edit the budget, targeting and creatives.
Certain options are no longer available for editing compared to when you initially created your Campaign, such as the campaign budget or campaign name.
Edit Budget
In order to edit your budget, you can pause your delivering Campaign, copy it and submit a new Campaign with new dates and adjusted budget.