To upgrade the LCM framework to the latest version, the administrator must go to the Settings page of the Prism Central UI, and then select the Upgrade Software option. This will show the available versions of the LCM framework, and allow the administrator to select the desired version and upgrade. Reference: https://portal.nutanix.com/page/documents/details?targetId=Platform-Administrator-Guide-v5_7:pag-lcm-upgrade-c.html

The Prism Central image repository is a centralized location for storing virtual machine images that can be used to deploy VMs to any cluster managed by Prism Central. When an image is imported into Prism Central, a copy of the image is made and stored in the repository, so that it can be easily accessed and deployed to any cluster as needed.
The original image file typically remains in the source cluster after it is imported into Prism Central, unless it is explicitly deleted. Similarly, the image copy in the Prism Central repository is not automatically copied to all clusters managed by Prism Central, but can be used to deploy new VMs on any cluster as needed.