A K8 was ordered by mistake, what does it take to make it a K9? I would prefer AES over DES for the VPN.
It seems that you are referring to K8 at the the end, you dont need to worry about this. ASA5520-K8 is only Based product ID and has nothing to do with license/image on the device.
If you need to use AES license for your VPN, you can obtain it for free from following link-
Once you get the activation-key for AES/3DES license, you can install it on your ASA using "activation-key " command in config mode. A reload is required.
I hope this helps.