If you have a SKU that has an incorrect grid associated with it, you will not be able to change the grid if there are any inventory transactions against the SKU. If you have a SKU that needs a new grid, but has inventory transactions preventing the grid from being changed you will need to:

Create the New SKU with the correct grid.

1. Load the wrong grid SKU on the Manage SKU page
2. Edit the SKU name appending old at the end
3. Save and copy the SKU
4. Enter the original SKU name as the name of the new SKU
5. Update the grids to the correct grids
6. Save the new SKU

Merge the Old SKU with incorrect grid into New SKU with correct grid.

1. Navigate to Inventory:: Stock Maintenance:: Merge SKUs
2. Choose the SKU selection method and click Next
3. Enter the Old SKU as the 'SKU to merge' and the new SKU with the correct grid as the 'SKU to merge into' and click Next
4. Map the old SKUs grid values to the corresponding new SKUs grid values and press Merge SKUs
5. Check your Report History to view the Merge SKU report that will verify that everything merged successfully