Keep them both! In fact, you will need both during the transition period while you convert your files from 9 to 10. The transition period should not exceed six (6) months. Deployment of the software after that period shall not exceed the licensed quantity of concurrent users of ExtendSim 10.
When you are ready to uninstall the ExtendSim 9 Network License Manager, see the FAQ Uninstalling the License Manager for an ExtendSim 9 Network License.