Upgrading a weapon consists of using materials to further increase its level and stats. It is very easy to do, however success rate is not 100%. To do so, the weapon's experience has to be full. It automatically gains exp as we kill enemies. (Click to enlarge picture)

Most upgrades require a combination of monster dropped items and gathering items. The gathered items are often the same, but may differ depending on which upgrade level we are at. For example, a level 1 saber may require copper bar, which is gained by mining level 1 -- but a level 2 saber may require iron bars (instead of copper), which is gained from mining level 2 -- albeit they both use items from the mining family.

These weapons require items from the following gathering families....

Forestry

• Baton
  
• Bow
  
• Boxing glove
  
• Dagger
  
• Staff

Herding

• Fan
  
• Musical instrument
  
• Syringe
  
• Wand

Mining

• Axe
  
• Saber
  
• Spear
  
• Sword

Once our weapon's experience is full, open the weapon upgrade window through Skill Interface (CTRL + X) > Everyday Skills > Weapon. From there we can select our weapon and see which materials are required. Proceeding with the upgrade will raise the weapon's level restriction by 5. Hence we should ensure that we're high level enough to continue equipping it. This process can be done 2 more times for a max upgrade of level 3.

The following may, or may not, increase our chances to produce better stats or increase the success rate of an upgrade:

• Using excellent quality materials
  
• Having alchemy of high level
  
• Having good provider's providence
  (we can discover our provider's luck by mousing hover our exp bar)

Images screenied in-game and edited by me