To purchase or upgrade a storage plan, press the Buy More Space button at the bottom of the SpiderOak application on your computer. This will securely log you in to your account on the SpiderOak website. Press the Upgrade Plan button. In Select a Plan Size, choose the plan you want, or if you don't see it, click on Show More Plan Sizes. Keep in mind that you are indicating the total amount of space that you would like in your account. You are not indicating the amount of space you want to add to your current plan.
In Select Payment Frequency choose if you would prefer to pay monthly or yearly. Press Next to advance to entering your credit card information. Press Next again, confirm your choices, and you're set.
If applicable, upgrades are pro-rated. If you are paying with a debit or credit card, then at the time of the upgrade you will be billed nothing. Then upon your renewal date you will be billed the pro-rated upgrade amount plus the normal renewal amount.