What change should be made to alleviate the performance problem?

Explanations:

Changing the Amazon EBS volume to Provisioned IOPS would improve disk performance but does not directly address the high CPU usage of the application. The latency issues are primarily due to CPU constraints, not disk performance.

Upgrading to a compute-optimized instance would provide more CPU resources and better performance for the CPU-heavy application. Since the application can only scale vertically, choosing a larger instance type with more CPU capabilities is the most effective way to alleviate the performance problem.

Adding additional t3.large instances would not resolve the issue since the application cannot be scaled horizontally (i.e., it cannot run on multiple instances). Therefore, this option does not address the high CPU usage effectively.

Purchasing Reserved Instances provides cost savings on the instance but does not improve performance. This option does not solve the underlying issue of high CPU usage and latency.