When importing Order Guides, if you have existing products, you have the option to either update only the bid price or overwrite the pack size for those products. If you check the box in Setup/Options, it will automatically overwrite the pack size, unit description, and All of it Packed in.
Overwrite the Pack Size with the Order Guide import
1) Click the Gear icon located in the upper right corner.
Click Manage Users & Units
Click Users & Connections
2) Click on Order Guides and check the box next to Overwrite pack size information:
3) Don't forget to click the green Save button.