So. I've been doing singing lessons for some time now, and it's going really well. I have slight problem though.

When I go to sing the high notes, I don't seem to relax in my throat enough to sing them. I go really tense. I do support from the diaphragm as well. Should I just keep on practicing the high notes I guess or?
Keeping doing the same thing won't change a thing. You need to figure out why it's not working well now (i.e. why you're tense), and then work on changing that.

I can't really give any substantial advice when I can't hear you... could you upload a recording of some kind so we can hear what you're doing?
I don't think it's a matter of relaxing the throat - the throat will be relaxed if you approach the high notes with solid technique. And as I said, I can't really help much with correct technique if I don't hear what you're doing...

General things I can say:
1) get your vowels right - in the higher parts of the voice you can't use all the vowels if you want to be loud (because of the way vowels shape you vocal tract). So you need to aim for certain vowels - I'd probably suggest "Eh" as in stay (without the "y" part of the sound).
2) Lots of twang - the higher you go, the more of twang you need. I won't get to the technical explanation of what twang is, but you can practice it by trying to sound like a duck, or a witch.
3) Move your support - you should feel that the support is moving, not locked or stuck in place. Having all the muscles there tense isn't any good (this was/is my big block). So just as a quick thing - the ribs should stay out, the abs under the navel should be moving in, and your back should be curving. And these movement's should be happening slowly.
4) and be LOUD. At least when doing this particular thing....

I don't know if these tips will help or not, mainly since I don't know what you're doing, and can't see how you react to them....