Guild Wars 2

I have Weapons and Armour that have ‘Unused Upgrade Slots’. What do I need to look for on the ‘Trading Post’ to ‘Upgrade’ these slots?

Runes and Gemstones for most armor pieces.
Jewels and Gemstones for most accessories. (Jewels are crafted from Gemstones by giving them settings.)
Sigils for Weapons.

Like Digital said. And here you will also get a link to give you a bit more info about them all.
http://wiki.guildwars2.com/wiki/Upgrade_component

Well this is still confusing to me. I have a staff with a Superior Sigil of Strength, so I tried to use a Sigil of Speed in the other slot, but it won’t let me. It wants to replace the other. I don’t get it.

You have to click the second unused slot to highlight it when adding a second sigil.

You need to click the unused slot when you try to add it. It will default highlight the first slot(which is taken by the Sigil of Str), just click the one below it.

Ah I’m an idiot. Thanks.