Hi,
When using a Boxcryptor account, you can simply install Boxcryptor on the computer, sign in with your credentials and then access your encrypted files again. All necessary information is stored (securely) within your Boxcryptor account.
If you did not sign out on the old computer, you can unlink your old device via our web interface so that you can sign in on the new computer:
https://www.boxcryptor.com/app
Best regards,
Robert