HEW is a complete IDE freely available from Renesas. It can be downloaded from the Renesas site or, more usefully, from the KPIT site.
If you have a copy from Renesas, it comes with compiler tools form Renesas and IAR. These are demonstration versions with time-limited and/or code size limiting restrictions. Since these pages describe the use of the GNU tools, there seems little point in confusing things by ending up with a lot of different tools installed.
The KPIT version comes without any compiler tools. the download is quicker and the tools can be added after installation. the most recent version(s) of HEW ship with an automatic updater. While this is generally a useful feature, it does mean that the updater will try and install updates for the tools that you do not have. There appears to be no adverse effect to this so you might as well let it get on with it.
I downloaded the HEW4.0 package from KPIT and ran the installer. If you have a previous version installed, this one will know and try to use the same folder for installation. I think it would be best to compleely remove all trace of any previous version to avoid any conflicts.
When the installer has finished, you will be asked to configure the autoupdater.
I set the Schedule to manual and then cancelled the subsequent update. The updater leaves a resident task going that can be used to update the software whenever you like. You may well prefer to allow automatic updates.
Dont bother to run HEW yet as it has no tools to work with. You should next install the Flash Development Toolkit.