For latest Plesk, it called Plesk Onyx. In order to upgrade to Plesk Onyx, it can direct upgrade to Plesk Onyx if your Plesk is version as below
Other then this, you need to check if your OS is as below
- Debian 7 & 8 (64 Bits)
- Ubuntu (64 Bits)
- RHEL / Centos (64 Bits)
- Virtuozoo Linux 7
If your Server OS is on 32 Bits, you can direct install NEW OS on new box.