Select the items, click Bulk edits, then Change Budget. In the Edit Daily Budget window you have two ways to adjust: enter a fixed amount that will be applied to all items, or use the minus and plus buttons to raise or lower each item's current budget by 10%, 15%, 25%, or 35%. Click Save to apply. On the Campaigns tab, the adjustment only works for campaigns with a campaign-level budget (CBO). On the Ad Sets tab, it works for ad sets with a daily or lifetime budget. Bulk budget editing is not available on the Ads tab, because ads don't have their own budget in Meta. To edit the budget of a single item, use the pencil icon in the Budget column of its row.