The DRO-550 runs OpenDRO software. The User's Guide for the DRO-550 is covered under the OpenDRO User's Guide. The DRO-550 Software Guide presented here only explains how to upload and verify OpenDRO onto the DRO-550 hardware.
The OpenDRO release images are available for download on the Files Section of the OpenDRO SourceForge project. Download the latest binary image, which is a file ending in .bin, that is appropriate for your hardware configuration. With a basic DRO-550 and if the latest OpenDRO release is 0.3.2, then you should download the file named opendro-dro550-base-x.y.z.bin where x.y.z are the the release numbers. If you have an LCD-200 attached to your DRO-550, then you should download opendro-dro550-lcd-x.y.z.bin. Note the "base" and "lcd" keywords in the file name. Save this file to your Desktop or somewhere convenient.