In the box w/ the MIFI, there should've been a little sheet of paper w/ your passkey and stuff on it. Read the very fine print under it & it has a HTTP address listed, just type that into your web browser and it will take you to info. about your wireless connections. After you put in your password, you can click on the button all the way to the right (can't remember the name, not at my home computer) then click on Diagnostics... The info. you're looking for is at the bottom & can be reset each month.
You can get your data usage by logging into your verizonwireless account and viewing the Mifi data usage (the MiFI is assigned a phone number, so select that instead of your cell phone's number). The usage tracking can be from a day to several days behind, so make allowances for that if you are nearing your limit!