Hello, i just paid for my current plan. and now i would like to upgrade, will i be charged with the whole new amount? or just the difference between the two plans?

Afaik, you will pay in full. Consider signing up for a new account instead at the discounted rate.

https://quickbooks.grsm.io/EU

Hello there, @useraccounting-team. I'm here to share some details when upgrading your QuickBooks Online (QBO) subscription.

Once you upgrade your subscription, you can see the charges for the new rate when processing. The calculation depends on its original amount and any discounts offered by the time your subscription starts.

To give you a further explanation of your billing charges, I recommend contacting our Customer Care Team. They have the tools to pull up your account in a secured environment and give you full details of your subscription.

To reach them, here's how:

1. Open QuickBooks. 
2. Go to the Help menu at the top.
3. Select QuickBooks Desktop Help. 
4. Type Contact Us in the search box. Then, click on Contact Us at the bottom. 
5. Select the way you wish to connect with support.

For more ideas about the things you need to consider before changing your plan, please check out this article: Upgrade or downgrade your QuickBooks Online subscription.

To tell you more about your subscription, you can visit this resource: Understand your QuickBooks Online subscription rate.

If you have other concerns about your billing and subscription, let me know in the comments below. I'm just around to help. Take care always.