If you have locked yourself out of user accounts or changed a setting that means you no longer have ip or snmp access then you will need to try to get a serial console connection on there i'm afraid.
Once you get a local console connection you may have access to then change the configuration with the admin login account.
If you are locked out of all accounts then you will need to go into password recovery mode. The following public knowledgebase article gives you details of how to do this:
Once you are in password recovery mode, as well as the reset password admin command, there are also 2 other commands that are not documented in that article that may be of use to you.
- “reset account” to clear all user accounts
- “reset config” to reset configuration to factory default.
I will edit the article to add those commands for the future.
Hope this helps