lol, well the line that starts around the middle of the graph, flat lines, and then falls at the upper rpms is your torque. That is the only part of the dyno that is actually measured, your horsepower (the line that starts low and continues to raise) is calculated based off your torque and rpm.
Horsepower = (torque x rpm) / 5252
What you can do is take your gear ratio, rear tire size, and find a "shift point calculator" (i came across this one, and it seems to be a very powerful program. I like it) to find out how to best approach your powerband.
Tire Size and Gear Calculator | GTSparkplugs
Taking an excerpt here, i will show you what i mean. Your horsepower seems to flat line right about 5800 rpm or so, so whenever we shift, we'd like to end up back in that flat spot (or at least as close as possible). Setting our shift point at 7500 rpms, we can see we really only fall back in that zone in the 4th to 5th shift. (6800 rpm is where it looks like your peak horsepower is in your dyno, that's why it shows shift points there as well).
Gear Change RPM drop (change @6800) RPM drop (change @7500)
*************************************************************
1->2 -2726 (To 4074) -3006 (To 4494)
2->3 -2339 (To 4461) -2580 (To 4920)
3->4 -1744 (To 5056) -1923 (To 5577)
4->5 -1307 (To 5493) -1442 (To 6058)
5->6 -2040 (To 4760) -2250 (To 5250)
*************************************************************
Really that doesn't do us much good, so lets just for ****s-and-giggles see what happens when we shift at 8000.
Gear Change RPM drop (change @6800) RPM drop (change @8000)
*************************************************************
1->2 -2726 (To 4074) -3207 (To 4793)
2->3 -2339 (To 4461) -2752 (To 5248)
3->4 -1744 (To 5056) -2052 (To 5948)
4->5 -1307 (To 5493) -1538 (To 6462)
5->6 -2040 (To 4760) -2400 (To 5600)
*************************************************************
Here we get it in 3-4 and 4-5, so that looks better right? Well, we're getting awfully hypothetical here, because we're assuming this engine will still have some decent airflow at 8000 rpms. Looking at the way the torque is tanking on the dyno however, i feel that's unlikely.
The best thing to do here then, is simply maximize our area under the curve. If you shift too early, you spend too much time climbing back up into your HP band. If you shift too late, you also run the risk of falling out of it on the other side. Its something that's neat and fun to play with.