Follow the below steps to edit your locked budget:

1. Navigate to the "Financials" page in the navigation bar.
2. Click the "Estimated Budget" tab.
3. Click the relevant cost centre item you wish to change.
4. Click the pencil icon for the relevant item line you wish to edit.
5. A window will popup prompting you to add in variation amounts to the line item.
6. Make variations as you wish, then click the orange "Save" button.
7. Once you have saved your changes, under "User Variations" you can view the budget changes you have made.