Your best bet is to export all email to a pst, uninstall outlook 2000 and install the newest version you want. You can install whatever version you wish, but keep in mind your system memory limitations. If you are installing the newest version of Outlook on an older system you may need to buy more RAM.
But the Q is upgrade not to change OL 2000 to another higher version. Of course it is good practice to take all necessary backups before doing upgrade ! in case of upgrade OL 2000….
Click Start > Programs > Windows Update
Click Check for Updates and Windows Update will now use ur Internet connection
Click Install and any upgrades that will be found for Microsoft Outlook 2000 will be downloaded and installed.