You can update by downloading the updates with
NUSGrabberGUI and installing them with the 5.5.1 version of wupinstaller (
included in this package.)
To use it, put the files from the folder with the .app files from NUSGrabberGUI and put them in SD:\install. Now just launch wupinstaller and it will install in the background.
Most of the times, waiting 15min for it to install in the background is enough. If you get a corrupted data error, you didnt wait long enough.