If you have changed/forgotten your admin password then you will have to complete what I consider a level 3 reset. A level 3 reset will restore all of the settings to the factory defaults.
Level 3 Reset
1. Power on the MiFi
2. Remove the back cover
3. Press and hold the Reset button next to the battery for 10 seconds
a. Watch the MiFi E-Ink display to see if all the icons are displayed
4. Release the Reset button
5. Reassemble the MiFi
6. Test your connection
Once you are able to sign into your MiFi you can change tour admin password under the Security Tab.