You have to contact the one that bought the license so they can login to licens center (https://license.episerver.com/).
In there you or they can find the license and just change ip or mac on it.
If you do not know who that person is, contact Episerver support
You may need to check the IIS compatibility if you are running CMS 5 (not 5 R2): http://world.episerver.com/documentation/Items/System-Requirements/EPiServer-CMS/System-Requirements-for-EPiServer-CMS-5-SP2/
You need to contsct your Episerver account manager to reallocate the licence. Account managers are based in the country/region of the customer so you should contact the country office where the client is based (assuming you are working for a client): http://www.episerver.com/contact/offices/all-offices/
Legacy documentation can be found here (use the dropdown list to find the exact version you are running): http://world.episerver.com/documentation/cms/?Version=5+SP2
I also recommend looking through this document with web.config-changes between IIS6 and IIS7 if you wish to go with Integrated mode, https://world.episerver.com/documentation/Items/Tech-Notes/EPiServer-CMS-5/EPiServer-CMS-5-R2/Changes-Between-IIS6-and-IIS7/
Could you please let me know how can I move/steps the existing Live EPI server CMS 5 site to new server.
Currently it is hosted under 32-bit Windows OS Server and IIS 6.0 version and we are planning to move to 64-bit server and IIS 7.5.
Please let me know how to move the license.