Upgrading from free tier to a higher tier.

You do not need to change anything, just ensure you've added a valid payment method in billing. You'll be billed at the end of the month for your usage, according to the pricing page of each service.

Then just create resources (e.g. EC2 instances, RDS instances, ...) from the console, the CLI or Cloudformation.

If you want, you can subscribe for technical support (either developer or business support), but this is not required to use the services you like.

Thank you for answering my question. The reason I asked this question is that I cannot access all the available resources because as a free tier user I can't use them. I can only use those instances that are available to free tier users. How can I change that? Thanks again.

There is no restrictions from AWS nor there is a specific "free tier user" type if you have a credit card in your account.

That said, it would be helpful if you specify the error you encountered when accessing the services.

Lastly, I don't think it would be an issue for you but do keep the service quota in mind.

Thank you. I realized after this exchange that when you start an instance that is no longer free, AWS gives a warning to let you know that you are entering a non-free tier. It is not an error and you can certainly proceed and start the instance without doing anything else, but you'll have to pay for it. I had not connected the dots until now and thanks to this exchange I think I understand the process.