Just unpack an image onto USB, insert USB in VU+ Solo2, restart the VU+ SOlo2 and after a few seconds there will be displayed the message: "Update, press power", acknowledge the flashing by pushing the power button on the receiver (not the remote control!)

The flashing starts and within a few minutes the flashing is ready and the receiver reboots

BTW: the unpacked image must be placed onto the USB including the folders, so the folder vuplus, in that folder there is a folder solo2 and in the folder solo2 are the files.