Open Blackhole is an image, like Blackhole, Openvix, etc..
Think of it as a Linux Operating System, on a PC, you choose the one you like.
To install an image, on the VU+ Duo 2, you download the image, intended for your specific receiver, in this case the VU+ Duo 2, uncompress it, and load the vuplus folder onto a freshly FAT 32 formatted USB stick.
You then turn off your receiver, using the rocker switch, at the rear, and insert your USB stick in the front USB port, behind the pull down flap, at the front right.
Turn on the VU+ Duo 2, at the rear, and press the front power button, near the front USB port.
The image will then start loading.
You will lose all your settings, so you might want to back up your channel list, using dreamboxedit, and note down any other settings, including your tuner settings.