Go to Downloads > Settings > Extension > Minimum/Maximum Quantities:
All settings are optional and should be numeric values.
Minimum order quantity
Customer must purchase no less than this quantity of items to checkout.
Maximum order quantity
Customer must purchase no more than this quantity of items to checkout.
Minimum order value
Customer’s cart contents cost must more than this amount.
Maximum order value
Customer’s cart contents cost must less than this amount.
Minimum order items
Customer’s must purchase total number of items greater or equal to this amount.
Maximum order items
Customer’s must purchase total number of items lesser or equal to this amount.