In order to change your Password, you must first log into your TGS player profile Click Here
On the left-hand side click Player Profile. Under Player Profile tab click on "Basic Info".
Click the line under Old Password then enter the old password associated with your TGS account. Next Click the line under New Password and enter the new password you want to be associated with your TGS account.
Once the Old Password and the New Password info are entered click "Save Changes" at the bottom of the page.