There are two places from which you can manage your sharing services. You can either click on your bit.ly username near the upper-right-hand corner of the page to go to your account settings (http://bit.ly/a/account), or you can click “Share Settings” beneath the sharing box on the main bit.ly page.
Choose either the Twitter or Facebook links to the right of “Add Account” to be redirected to the corresponding service. Log in to the account on that service from which you wish to share and click to authorize your bit.ly account to have OAuth access to that other account. This way you won’t ever need to share your Twitter/Facebook credentials with bit.ly, bit.ly will remain authorized if you change your Twitter/Facebook password, and you can revoke bit.ly’s access to your Twitter/Facebook account from either your bit.ly account settings page or Twitter’s Connections page / Facebook’s Applications page.
Once this process is complete and you are redirected to the bit.ly site, you can click “Add Account” again to authorize bit.ly with additional Twitter/Facebook accounts.
Alternatively, click “Remove” next to the account you wish to unlink and that account will be deleted from your list.
To temporarily activate/deactivate sharing from each service, click the “Sharing off”/”Sharing on” links next to each account.