I suggest that we rewrite the first and second paragraphs as follows:
Advertising is displayed on LiveJournal to support site operations and to ensure that there is an account level available to users free of charge.
In exchange for viewing and displaying advertising, Plus Accounts gain additional features and storage space in a manner similar to Paid and Permanent Accounts. If you have an Early Adopter or Basic Account, you can join or leave the Plus level at any time. Paid and Permanent Accounts can not switch to the Plus level.
If your personal account was created on or after March 12, 2008, you cannot switch to the Basic Account level. If you do not wish to see ads on LiveJournal, you will need to upgrade to a Paid Account.
To change your community's account level, use the Account link on the Manage Communities page. You may change your community's account level at any time. For more details on what ads you will see at each account level, please see the list below: