How do I close my account?

You can cancel your account at any time by logging into the Member's area, and clicking on the "Account" sub tab. From there, there's a cancel account link. If canceling within the first seven days, be sure to ask for a credit on the cancellation form. You can also remove all Linodes from your account via the "remove" link on the Linode Manager tab. This will issue a pro-rated credit to your account, which will be applied to any future invoices and effectively allows you to keep a Linode account open without incurring charges.

You can always downgrade your Linode, a 512 can host a lot more than most people might expect ^_^

Anyhow, to your question at hand, don't quote me on this because I might not be correct, but I believe the way it works is that the amount that you'll get back is calculated as if you hadn't gotten the 10% discount.

As in:

- $20/mth linode
- 12-month pre-pay, 10% discount
- 20*12*.9 = $216 paid
Canceling after 6 months:
- 20*6 = $120 consumed since discount is cancelled by breaking the term
- 216-120 = $96 refund

But, I could be misremembering all this!