1. On Meal Prices tick the meals (or the header checkbox) - the counter shows "3 Meals selected" and Bulk Edit Pricing becomes active.
2. Click Bulk Edit Pricing. Choose By Value ($) or By Percentage %.
3. Enter the change for Selling Price, Surcharge and Original Price of the default portion and, in Portion Prices, the Upgrade and Surcharge change per portion size. Leave 0 for fields you do not want to touch; negative numbers decrease.
4. Click Submit.

The amounts are added to each meal's current values (or applied as a percentage of them). Sprwt keeps the rule that the selling price must stay at or below the regular price: if a computed selling-price or regular-price change would break that for a given meal, just that price is skipped for that meal - its other bulk-edited fields (surcharge, portion prices) still apply.