Hi Amanda,
Thanks so much for reaching out–great question! An upgrade to an existing license will effectively “reset” the renewal date of your licensing; your upgraded license will be automatically extended out for one year following the date of your upgrade. For example, if you have a Personal license that is due to expire on June 1, 2017, and you purchase an upgrade on May 15th, 2017, your new expiration date will be May 15th, 2018, and you won’t need to renew prior to that date.
I hope that helps to clarify things a bit here! Thanks again, and let us know if you should have any other questions!