I think that your problem is a bit difficult to help with, since not a lot of users actually own Vocaloid 4.5 for Cubase (normally people would be jumping to help anyone with questions). Rather, they usually have the normal 4 or 5 Editor.
Anyway, I don't personally own 4.5, but I did try to look up about how to use Vocaloid 4.5 for Cubase. I will write what I can and hopefully it can get you in the right track.
Here are some FAQ answers by Yamaha for 4.5:
List of Search Results for 4.5 page1 | support | VOCALOID
Selecting the Vocaloid VSTi + Adding track + launching Vocaloid 5
Another tutorial:
After seeing that tutorial, it looks like the pop-up for your VSTi is Vocaloid 4, but the one in the video says Vocaloid 5.
I found a video tutorial in Japanese by Yamaha about how to use it (I speak Japanese, I can translate any part of this video if needed). This one is specifically for Vocaloid 4 in Cubase, it says to add an instrument track, select VOCALOID Inst, he drags the piano MIDI down to the VOCALOID track. To edit the lyrics, he had to go to the menu > MIDI (M) > Open VOCALOID Editor (V).
Could you please let me know if any of these tutorials helped or if you're still having trouble?
You should also know that Yamaha DOES provide customer support in English and I encourage you to contact them if we can't figure this out on VocaVerse. Go to
this page and scroll to the bottom to agree, which takes you to a form to fill out. They usually reply in a couple of days.