If you already have the game it should auto patch when you launch it (run irisclient.exe)

If you quit long ago and haven't patched in ages, you should redownload.

If you are talking about the recent huge update, sedy had some links to the client at that time http://noscrubs.net/discussions/recent-discussions/update-28-03-15 BUT you will still need to patch (just shorter) since there were some bugfix since then.

For more troubleshooting http://noscrubs.net/discussions/launcher-errors-need-a-manual-patch