Yes, you can.
You can upgrade the application you have purchased to a new version while your license is valid.
By purchasing a Kaspersky Lab application you purchase the right to use it until the license expiry date (for 1 year usually). The license expiry date is specified in the key file or activation code provided with the program.
A key file is a file with the extension .key (XXXXXXXX.key). It serves for activation of an installed Kaspersky Lab application.
An activation code is a charset of 20 symbols divided into 4 sections 5 symbols each (XXXXX-XXXXX-XXXXX-XXXXX). It is an alternative method of activating an installed Kaspersky Lab application.
Kaspersky Lab software does not function unless activated with a key file or an activation code.
While your license is valid, you can upgrade a purchased application to a new version (as new versions become available). New versions feature additional functions and have errors fixed.
Example 1, you have purchased Kaspersky Anti-Virus 6.0 for Windows Workstations. Its license is valid for 1 year. The CD you have purchased contains version 22.214.171.1247, which you have already installed. Some time later Kaspersky Lab releases a new version of the same product – 126.96.36.1994 (Kaspersky Anti-Virus 6.0 for Windows Workstations R2).
Given that your license is still valid by the moment the new version is released, you can download it, install on your PC, and activate using your existing key file, thus upgrading your Kaspersky Anti-Virus version.
While Kaspersky Anti-Virus for Windows Workstations 6.0.3.x license is valid, you can upgrade to the version 6.0.4.x and keep using your existing key file / activation code.
You can find a guide on version upgrade process either in the correponding section of the Knowledge Base, or in the file release_notes (found in the application distribution package).