Log into your client area by whogohost.com/host/clientarea.php. Once logged in, click on Hosting & Services and then select My Hosting & Services. Choose the account you want to update by clicking on it. You will be redirected to a page that shows the details of the hosting account. On the left-hand side of the page, there is a section with the title "Actions". Select the Upgrade/Downgrade option under it. Choose the new plan you wish to upgrade to but do not change the billing plan.
If you have issues with the upgrade, feel free to contact our support department at email@example.com for further help. Custom plan can be also created on demand by customer.