I have upgraded the free subscription to basic pay as you go subscription. After upgrade, the option upgrade subscription is not showing in overview page of subscription.

If you have upgraded your Azure subscription from a free account to a basic pay-as-you-go subscription, the option to upgrade your subscription may not appear immediately due to the nature of the subscription type. The upgrade option typically becomes available only for certain subscription types, and if you've already upgraded to a pay-as-you-go plan, you might not see the upgrade option again unless you are eligible for another upgrade or switch.

If you are looking to switch to a different offer or if you believe there is an issue with your subscription, you may need to contact Azure support for assistance. They can provide guidance on your specific situation and help you understand your options.

References:

• Upgrade your Azure free account or Azure for Students Starter account
• Change your Azure subscription to a different offer