If you're a Team Member and want to post a shot to your Team page, sign in and go to upload as usual, then select the "Publish as" team option at the bottom of the upload screen. Shots posted this way will appear on your personal account and linked to the team as "by [you] for [team]." The shot will appear on both the Team profile as well as their own, with dual attribution.
As a Team Owner, in cases where you want to upload to the team account only, you would do this by 'using Dribbble as' the team and upload directly to that account.
Members can also retroactively attribute shots to the team by following the “Edit” link from the shot page.