If you would like to change the AWS EC2 Instance Type (Size) for Access Server on the AWS
If the Access Server uses the fixed license key model, the existing fixed license keys have to be reissued.
If the Access Server uses the Tiered Access Server or AWS OpenVPN Access Server BYOL (Subscription) there shouldn't be any conflict with licensing while the customer is updating the instance type.
The AWS guide is Here for the EC2 Instance Type change.
If you have an Amazon AWS tiered instance, pre-licensed with “xx connected devices”, you don’t need to worry about licenses. It is taken care of internally by Amazon’s systems that handle licensing and billing. Simply upgrade the Access Server package itself.
Please follow the AWS guide Here to proceed with the EC2 Instance Type change.
Back up your settings, check server and client compatibility "Guide"