Box provides an excellent collection of documentation:
For issues using M+Box, please contact the ITS Service Center
If you currently have a Box account using your @umich.edu email address, you will not be able to create a new M+Box account in the University domain.
WARNING: Do not delete your personal @umich.edu Box account in order to create an M+Box account. Users who delete @umich.edu personal accounts without first changing the email address will be unable to create an M+Box account following the normal signup process. If you have deleted your account, please contact the ITS Service Center for assistance.
Converting your M+Box account allows you to maintain any collaborations you have and give you the benefits of M+Box, which will soon include unlimited storage.
Your personal account will not be impacted. However, you must set up a M+Box account to have access to the M+Box enterprise account features.