The least you need to do then is disable or upgrade the "Forgot Manager Plugin" as early versions of this had a security flaw
To disable:
Go to Elements > Plugins
Click on "Forgot Manager Plugin"
Then click "Plugin Disabled"
But it sounds like this is your only way of getting in...
And if you can't get in you can't enable it to get in!
You can re-enable it each time you get in by enabling it in the database
in the table [Something]_site_plugin ( where [Something] is probably "modx" ) and updating the disabled field for the plugin
To upgrade
The latest version is here
http://modx.com/extras/package/forgotmanagerlogin
but it says it requires Evolution 1.0.x or greater so you might be out of luck
But your site is at risk of being hacked without action.
Mike