Just go into your Stargate control panel and make sure the the domain name that you want to transfer is unlocked and that the whois information, especially the administrative contact's email address, is all valid.
Then go the the NEW registrar of your choice and initiate a transfer from there. You do have to pay for an additional year's registration fee at the NEW registrar. Then you will probably receive a couple of emails verifying that you really want to transfer the domain... you usually have to click on a link to verify them - but sometimes you don't have to do anything.
Then in about 3 to 7 days, your domain should be in the NEW registrar's control panel where you want to go and then "LOCK" the domain again to prevent someone else from transferring it away from you.
You shouldn't have any problems with Stargate letting go of the domain. But you always want to make sure that you keep your domains paid up-to-date at Stargate as they used to have a $200 redemption fee with no grace period when the domain expires. (Please note that it's been over a year since I had any Stargate domains - so this info might be rusty).
You may delay, but time will not. --- Benjamin Franklin