@el_jaynado
If the accounts are linked changing the password for your origin will also change it for your swtor account so the person who was in your Star Wars account will no longer have access. I would also recommend running both a virus scan and a malware scan on your computer just in case.
In regards to deleting your star wars account, unfortunately there is no way to just delete the Star Wars account without also deleting your EA account as well. You can add a security key to your star wars account for example using the mobile app, then uninstall the app once you do so which will prevent further access.
Other then that there is no other option to delete just your star wars the old republic account.