You could use this guide i think
link.
Its pretty straight forward, just skip the apache installation part and if you are running CentOS 6.x follow the fedora instructions.
Just change the listener in the admin panel to 8080
There is one more thing you need to do that is to edit the
/etc/varnish/default.vcl file.
Do the following changes:
nano /etc/varnish/default.vcl
Change .port = "80"; to .port = "8080";