Rune overwriting

I'm wondering how exactly does Rune overwriting work? I heard that higher runes take precedent over minor ones superior>major>minor if you use multiple runes on the same item.

Basically my situation is this: I currently have a flame's eye of minor fire magic, and I just got a major fire magic rune. I want to put the major rune on the same flame's eye without crafting a new one. Can I just put it on normally and just have the major rune "overwrite" the minor one?

It's just that I also read somewhere that the old rune sometimes overwrites the new rune or something like that, which got me a little worried.

Thanks

yes major will overwrite the minor new overwrite old, did multiple of times
I was in the same situation for fire eye...but i preferred to craft another eye
so now i've one minor eye (+1+1) and another one +1+2 -50 health hehe