I have just encountered an enchanting problem...I enchanted my recent weapons (skyforge steel war axe and orc war axe) and whatnot, a fire enchant doing "+12 fire damage" and the same but a frost enchant for the orc weapon, but I then found a weapon that did +35 fire damage (or something massive like that) and I was like WHAAAAT! So I went to disenchant it, but when I did it said "you already know this enchantment" or something?! So it's like, once you get an enchantment, you can't get a better one (even for other weapons). I've looked at the perks, I've tried different soul gems (which just make it last different times)...so...if anyone knows, then cheers.

Yes, sadly, once you enchant a weapon, that enchant can't be removed.

This is sad when it involves one-off weapons like the skyforge steel weapons.

Disenchanting is solely for learning a new enchantment type.

You need better perks and better skill.

Hmm, I just realised I didn't quite word something properly, I also meant that I have a saved enchantment to use on other weapons (as in the +12 fire damage) but that can't be replaced by the better fire damage enchantment, to use on other weapons, but I didn't even know you couldn't re-enchant weapons...that svcks :/

As your skill improves you can apply the enchantment "better" yes. That is to say, if you take a +15% lockpicking ring and disenchant it, it doesn't matter that it was a +15, a +5, or a +20 variant. You just learn "Fortify Lockpicking" and when you apply the enchant yourself, it scales based on skills, perks, active effects (potions), and the soul gem in use.

Oooh, ok, so if I just keep doing enchanting I'll eventually be able to replace that one I'm guessing?/hoping? Well, I can use some perks anyway to get it from 12 to like...30, so it's fiiine. Thanks for the help!

No that 12 enchant will always be there. You need to grab a new weapon to throw a different enchant on it. I'll give you a heads up though... the elemental fury dragon shout works better than any enchantment(and it doesn't work on enchanted weapons).

Skyforge steel weapons aren't one off. You can buy them from the guy any time you want.

If you enchant an item when you have a very low enchantment level, does that items enchantment power increase once you level up your enchantment?
if not, if you increase your enchantment level, do new items you enchant now reflect the new power level or is it stuck using the level of the enchantment when you first learned it?

I have 0 perks in enchantment so when I create new weapons, I have like +5 frost damage. thats it. Am I screwed for frost damage or will it get better once I put perks in enchantement?

You'll get better ratings once you get better. But the stuff that you're making now can't be improved.