Where can I edit the budget for my campaign?

Your campaign budget can be updated under campaign settings in the campaign edit page.

To edit a campaign:

Log in to AdRoll and navigate to Campaigns on the left side menu.
On the Web & Social page find the campaign that you want to adjust.
Click ellipsis next to the campaign name and select Edit.
On the Campaign Settings page, scroll down to Campaign Budget settings and click.
Update the Daily budget field as shown in the screenshot. Once done, click Save.

To learn more about editing the campaign, check out Edit Your Campaign.