ResolutionFirst, the latest version of OS template should be installed on Virtuozzo server (if it is not installed yet), please refer to this article for intructions - http://kb.swsoft.com/en/1451
After desired version of OS template is installed, for example, to upgrade VE #101 to the latest version of Fedora Core 2 OS template, just run the following command:
# vzpkgadd 101 fedora-core-2
If VE #101 was created on some earlier version of fedora-core-2 template, it will be upgraded to the latest version. Application templates can be upgraded in the same way.
The other approach is to upgrade VE using a standard system utilities such as yum and up2date in Redhat-based systems and then use the 'vzcache' utility to move common files to the template area after upgrading. The point is that for the VE owner, their VE is just a Linux system (say, Redhat) which can be updated in a regular way just like any other Linux system. If VE owner needs to install some program, they can just download it to the VE and install using 'rpm' utility inside it.
You should note that the size of a VE on the hardware node will be probably increased after that operation and 'vzcache' utility can move files from a VE private area to a template area, thus minimizing disk space usage of this VE. This is especially effective in case more than one VE have the same non-templated files in their private areas.