from the FAQ:
Q - Do I have to be a U2.com Subscriber to participate in the U2.com Tour Ticket presale?
A - Yes, this pre-sale is only for Subscribers of U2.com who have purchased a Subscription. Subscribe here. If you have an existing account, but it has expired, Upgrade here. Or, if you are a paid up subscriber but wish to renew your subscription now, renew here.
Q - When is the latest I can join U2.com to be involved in the Internet ticket pre-sale?
A - Anyone who is a current Subscriber to U2.com can participate when ticket pre-sales take place but those who have been Subscribers longest get the earliest opportunity to enter the pre-sale. 'Experience Subscribers' have access starting on the morning of Day 1 of the pre-sale, 'Innocence Subscribers' have access from the morning of Day 2 of the pre-sale. The pre-sale for each concert closes at Noon / Midday on Day 3. The public ticket sale will start after Day 3 of the pre-sale. The exact times for access are made available on the tour page of U2.com.
Q - How do I know what pre-sale priority group I am?
A - There are two groups of subscribers taking part in the pre-sale and the email you receive with your pre-sale code indicates which group you are in.
Our 'EXPERIENCE' group of longtime subscribers (those who were current, paid-up subscribers on 09/09/2014 12:00:00 PST) have access from the first day of the pre-sale. Your unique pre-sale access code will have a prefix of U215A...
Our 'INNOCENCE' group, who joined as new subscribers or upgraded an expired account after the release of the latest album in September 9, 2014 12:00:00 PST, enter early on the second day. Your unique pre-sale access code will have a prefix of U215B...
Only after this does a public onsale begin. (You may also find which priority group you are in displayed on the Account Info page when logged in.) Please Note: We do not change your subscription category. No exceptions will be made.