In order to do that you can use these reports:
1. Deployment projects
. In this report you can remove the hosts you want to replace from the scope and check what resources will you need for the new hardware.
2. Datastore Performance
and Datastore Performance Assessment
. These reports will show how much IOPs you're currently consuming, so that you could plan the purchase of the new storage device.
3. Host Performance
. Use this report to review your CPU usage on the host you want to upgrade.
4. Multiple Clusters Performance
. If you want to upgrade the entire cluster, then this report will give you the details about hosts performance, including network data transfer stats.