To manage information of your company and permissions for product submission and sandbox access, you need to be admin of your company. Admin, by default, is the person that "creates" the company when first requesting a sandbox

In case this was done by one of your colleagues, the admin can also make you an admin for your company. 

To make someone else admin of your company, the admin can login to the portal and go to "my account > settings". Then navigate to the "permission tab". In the permissions tab the admin can see the list of all users enabled for his/her company. If the user is not listed here, the admin can just add a user to the company.
When the user is listed, just click on the 3 dots at the end of the line, and click "make admin". In the pop-up window, simply click "grant". Confirm your changes by clicking the "save"-button at the bottom of the list.

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