The crucial thing to know is the impedance rating of both the speakers and the amp. The speakers apparently have 8 Ω. If the amp were rated for 195 W at 8 Ω, then it would – as might be expected – only be safe to turn it up to 20 %. (On a decent logarithmic volume pot, this would actually be something like 11 o'clock; no idea how those 10 ticks on your amp are graded).
Likely though, the amp is rated at a lower impedance – typical are 4 Ω or 2 Ω. That's no problem†, but it means the amp will actually never be able to attain its full output power if you connect a 8 Ω speaker: at its maximum peak voltage, the current will only be half or ¼ of the maximum it could supply. So if the amp is 4 Ω, then 40% volume are save, if it's 2 Ω, 80% are safe.
Again, I can't tell you which setting of the volume control this corresponds to. This control is only meaningful with respect to a perfectly levelled input signal anyway.
40 W is certainly enough to create quite some noise, so if at the moment you find it too quiet then it's probably safe to turn it up further. No guarantees though, I can't know how loud you like it!
†It would be a problem to operate a 2 Ω speaker on a 4 Ω rated amp though: it would damage (or, with decent modern models, shutdown) the amp.