To create more than one pricing period, or to change ticket prices based on the number of tickets in a transaction, use the Advanced Pricing settings at Event Dashboard >> Tickets >> Advanced Pricing

You can create multiple purchase periods if you want the price to change as the event gets closer. The second part of this section asks if you want ticket prices to change based on the number of total tickets in the transaction. (For example, you might choose to sell tickets for $10, but discount them to $8 if someone buys five or more tickets in a purchase).