Upgrading your subscription has an intimidate affect on your quota. Remember you are upgrading your existing quota not purchasing more credits.
If you are on a 5k plan, (so you have 5,000 emails to validate each billing cycle) and you have used 4,856, you now only have 144 emails remaining. If you now upgrade your subscribed plan up to a 10k plan, you can now verify a maximum of 10,000 this billing cycle. As you have already used 4,856 this would leave you with a quota of 5,144 to use this billing cycle.
Purchase the right plan by subtracting the quota you have already used from the total of the plan you are upgrading to. So if you upgrade to a 10k plan, you would have 5,144 emails left in your quota for the period. (10,000 - 4,856 = 5,144).
You can upgrade your subscription at any time by using the Upgrade button from within your account.
Login to your account and follow the instruction below.
Step 1. Click on the "$ Buy Now" Tab located at the lower half of the list on the left hand side of the page and then Click on the "Upgrade" button.
Step 2. Click on the "Continue to billing portal" button.
You will be redirected to the Customer Portal, as shown below.
In the Subscription section (6th Section down the page) you will see and Upgrade/Downgrade link at the top-right of the section.
Step 3. Click on the Upgrade/Downgrade link and you will be redirected to Change your plan page.
Step 4. Choose the new plan you desire and click Save and Continue.
If the process has been successful you will be redirected back to the Customer Portal and there should be a message in green at the top of the page “Successfully updated your subscription”.