You have the base installation.
Patch 4 is the most current patch and is downloadable from the portal with your grant number.
Upgrading information from 4.5 to 4.6 should be included in the installation documentation for 4.6
(Can't give any persoanl advice as we can't upgrade as we have products that currently are incompatible with 4.6 and are awaiting patches for them)
Thanks for your quick reply