This depends on how you're setup right now. If you have an account with access to Configuration -> User Access & Roles then just follow this article:
http://www.lansweeper.com/kb/102/restricting-access-to-the-web-console.html. The article is slightly outdated, we've recently added the option to add Active Directory groups to roles.
If you don't have a user with access to configuration, then you can give access to all users by doing the following:
- If you're using IIS Express: Run Program Files (x86)\Lansweeper\IISexpress\ExpressAuthentication.exe and make sure anonymous access is enabled
- If you're using IIS: Make sure anonymous access is enabled and Windows authentication disabled
- Enable the built-in admin using this tool: Program Files (x86)\Lansweeper\Service\ResetWebUserRoles.exe
Make sure to enable authentication again after you give yourself the required roles.