This post outlines and answers all of the questions about upgrading your existing SharePoint 2013 Free Forever hosting plan to a paid plan with unlimited users and more storage space.
Step 1 is to click the plan that you want to purchase on our website: http://sharepointhoster.com/sharepoint-2013/sharepoint-2013-foundation-plans-and-pricing This will take you to our checkout cart. If you selected the wrong plan, you can easily change your SharePoint 2013 foundation hosting plan by clicking the dropdown menu.
All of the hosting plans come with 1GB of storage by default, but you can check the additional storage option to add additional storage to any of these annual plans. You can also select to setup a custom domain name for your SharePoint site during checkout. Remember that you can always upgrade your hosting plan with these features at a later date via our upgrades page: http://sharepointhoster.com/sharepoint-2013/sharepoint-2013-foundation-plan-upgrades
After selecting and confirming your hosting plan, click next.
On this page you will need to fill out all of your billing information under the New Account section. DO NOT click the (Click here if you already have an account) link - that is for people that already have a plimus billing account - not a free hosting account
To upgrade an existing SharePoint 2013 Free site, you need to fill out the Existing or Preferred Site Name field under the additional info heading. Type in a new site name to create a new site or type in your existing free site url if you want us to upgrade that site. Example: If your site url is http://mysite.sharepoint99.com - simply type mysite or mysite.sharepoint99.com in this field and we will automatically upgrade that site.
Once you have filled out this page and selected your payment method, click Next.
The final page confirms all of your information and asks you to put in your payment information (Credit Card in this example). When you are ready to submit your order, click submit and we will upgrade your site within 24 hours. If you have any questions about our secure checkout or sales in general, please submit a ticket or chat with us online.