If you find your Plesk or VPS operating system to be obsolete and no longer supported, you may need to transfer your websites to new VPS with Plesk. Transfer process in general consists of the following steps:
1) Subscribe to new VPS with up-to-date OS and Plesk software.
2) Perform regular migration via Plesk Migration & Transfer Manager, make sure domains are consistent and functioning fine on new server.
3) Delete the hosting of migrated domains in POA CP. Note, POA will also delete the contents of domains from source server and remove DNS zones from POA-managed nameservers.
4) Add web hosting for migrated domains back, but choose hosting resources from new subscription.
5) POA will configure DNS zones automatically using new Plesk as master nameserver.
Please refer to the following article to find out interoperability information for different versions of Plesk and POA software.