There are manuals available online that can be ordered (usually run around $10-15 for download).
Most of the vintage machines are very similar in terms of threading and function. I don't know about this specific model, but on some machines I have found the feeddog up/down lever inside the bobbin area. Whether it's a knob on the outside of the machine or a lever on the inside, it's usually marked with a little teeth symbol something like this: ^^^^/^^^^
Judging by a Youtube video on this model, I'd say it's likely that the feed dogs on it can be dropped. Google and check Youtube for more info.