Heaven Stones are considered to be the best way to upgrade weapons and armor past +3. Heaven Stones have a higher success rate when upgrading, but they are also considered a rare drop and can be expensive to purchase from players due to their rarity. Heaven Stones do not have levels and can be used to upgrade any level item, removing the restrictions that apply to Smelting Stones.

Acquisition of Heaven Stones
Heaven Stones can be purchased from other players or can be obtained from any mob in the game. Heaven Stones are considered a rare drop and are thus expensive to buy from other players. You can also buy Heaven Stones from the item mall - a nice quick way of gaining Heaven Stones for mass upgrading.

Using Heaven Stones to Upgrade Weapons and Armor
To use a Heaven Stone to upgrade an item, equip the item you want to upgrade, click and drag the Heaven Stone to the item, then click to confirm that you want to upgrade.

Success Rate of Heaven Stones
Heaven Stones will not always succeed to upgrade items, but failure to upgrade using a Heaven Stone does not always result in the destruction of the item.

Heaven stones have a 50% chance of success, which doesn't sound great, but it makes a huge difference. Of course, this also means that they have a 50% chance of failing. Failing with Heaven Stones does not always ruin the item like Smelting Stones do. If you fail an upgrade with a Heaven Stone, one of three things will happen:

1) There will be no change in the item but the Heaven Stone will be destroyed
2) The item is downgraded by one (ex: +5 item becomes +4) and the Heaven Stone is destroyed
3) The item and the Heaven Stone are destroyed in the process

NOTE: Go to STRATEGY SECTION and click the section "How to Upgrade with Heaven Stones." This is the technique and secrets revealed that no one seems to want to tell others. Remember, be flexible and patient now. One person put on the forum that my technique did not work, because he failed 7 times in a row. I was really sorry for the person as he did not read the section well and I told him as such. You have to read it more then once to fully understand what I am saying. If you fail twice in a row, wait and try another day. That is what I do. I have succeeded upgrades on 2 armors in a row and the 3d one failed. Then for me, upgrading shirts is always harder to upgrade then others. One shirt I failed like 5 times, till i got the shirt upgraded. Who knows? But that was like a 2 week project too, lol.