cannot install orcad 16.6 Lite, please help me

Why would you want to install the Lite version when you already have an updated version of the same tools installed? The 16.6 tools will run in Lite mode if you don't have a license, use allegro - orcad at the Command Prompt to start PCB Editor in Lite mode, if required. If you have a licensed installation and want to start the tools in Lite mode anyway, rename the CDS_LIC_FILE Environment Variable so that any license will not be found and you will then be prompted to start the tools in Lite mode.