I'd be glad to assist you with upgrading your QuickBooks Online (QBO) Simple Start plan to Essentials, @hamdyaboelghet4-
If you upgrade to QBO Essentials, your billing date or cycle will remain the same, but the price will be adjusted according to the new plan. Moreover, you'll also have access to additional features and functionalities with the Essentials plan by navigating to the Subscriptions and billing menu.
On the upper right corner, look for the Gear icon.
Choose Subscriptions and billing under Profile.
In the Billed to you section, select Upgrade your plan.
Select Choose plan under the Essentials version. This page also indicates your rate per month.
From there, you can follow the on-screen steps to upgrade your plan.
Once done, you're now ready to start using the QBO platform. To assist you in setting up your company file, linking your accounts, importing your lists, setting up taxes, and managing your users, I encourage you to check out this article for a comprehensive guide: Get started with QuickBooks Online.