Hi @Suliyat Rafiu ,
what does "am unable to upgrade it to pay as you go" mean? Any error message is showing up?
The process of upgrading the Azure Subscription is described here: Upgrade your Azure free account or Azure for Students Starter account
If the upgrade is not working the best option is to open a support request with Azure Support:
Create an Azure support request
Azure Billing and Subscription support is offered by Microsoft by no cost and it's for free.
Source: Azure Support plans
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Regards
Andreas Baumgarten