Download and read the installation guide. It answers all your questions.
You need to download the correct SWPM to get the EHP6 installation option.
You don't need to uninstall anything. If your requirement is to add an additional application server to the existing instance then you just need to run the sapinst on the target node and install it.
The prerequisites are mentioned in the installation guide.
The /sapmnt/SID filesystem from the PAS server should be mounted on the installation node.
You will also need to download the Oracle client media and provide that during the installation.