I'm trying to install VPN but I can't continue with the installation because everything is greyed out or only the AMP is available.
This happens when there is a previous installation of VPN on your machine.
First check if it is still installed:
If nothing is there here is the procedure for manually uninstalling the AnyConnect client:
Run the following shell script from the Terminal:
$ sudo /opt/cisco/vpn/bin/vpn_uninstall.sh
You will be prompted for your password. Once you enter it, just follow the steps and reboot.
If you are still having problems try this from the terminal.app and reboot:
sudo pkgutil --forget com.cisco.pkg.anyconnect.vpn
Here is a more detailed page for assistance.