Log in then download and install the latest version from the PolyBoard download page or the StairDesigner download page.
By default, the installer will copy the library files onto your desktop into this folder:
polyboard-version or stairdesigner-version
The new install will overwrite all files if this folder already exists. If you want to keep the old libraries, rename the folder before installing the update.
Please also note: you must be using the latest version of the software to use the latest version of the libraries.