Number of Windows 8 Pro licenses per computer

Solution 1:

You need to purchase an upgrade for each PC that is eligible for an upgrade. You cannot use 1 upgrade on 3 PCs.

Example: If you have 3 PCs that are eligible for upgrade, and you have purchased an upgrade for each of them then you can upgrade them. If you have say 6 PCs eligible for upgrade, you can only purchase 5 upgrades at the special price, because the discounted upgrades are limited to 5 per customer. You will have to pay the regular price for each license over 5.

Solution 2:

You have to purchase separate license for each PC you upgrade:

The promotional price is limited to one upgrade per PC…

 
And you can upgrade a maximum of five PCs by promotional price:

…and a maximum limit of five upgrade licenses per customer.

If you need more upgrade licenses, you would have to buy them at the regular price.