First determine whether you want to change the target ACoS or budget for a Sponsored Products, Sponsored Brands, or Sponsored Display goal.
Then click on the appropriate tab.
Change target ACoS
Find the goal you want to edit from the Goals list and hover next to the number you want to change to find the pencil icon.
Click on the pencil icon.
Enter your new target ACoS and click Confirm.
To change the budget, you can hover next to the budget of the goal you wish to edit and click on the pencil icon.
Enter your new budget and click Confirm.
Alternatively, you can make the same changes in the goal deep-dive under the configurations panel and click Update when done.
The same step follows to change target ACoS and budget for SB and SD goals.