Our SSD packages are only available in our Texas data center. Since your current VPS is located in our California data center, if you want to move to an SSD, you would need to place an order via our website for the SSD-2 and the signup invoice would need to be paid at the time the order is made. You'll get all new IPs with the new SSD.
When the SSD has been provisioned and you've received the welcome email with your login details, you'd need to open a ticket with our Technical Support team and request the migration from your existing VPS to the SSD. After the migration is completed, you will have to let us know here in Sales that you're ready to cancel the VPS. When we cancel the VPS, we'll add a prorated credit to your account for the balance of the current billing period so you'll only be paying for both packages while both need to be active.
Once you've reviewed the above information, let me know if you have any questions or if there's anything else I can do to assist.