In general, you should be able to buy a Web license and add it to the other licenses on your License Manager, or to the node-locked licenses on your local machine.
To perform Web testing, you would need to have installed the Web module on your machine. Check "File | Install Extensions" to make sure the Web extensions are present. If not, modify your TestComplete installation to install the Web module.
On the machine that is to serve the license either use the License Manager to activate the license, or use TestComplete "Help | Activate or Deactivate License...".
See the Activating Licenses topic for more information.
