First, there is no way that you got UV "Increased Normal Damage" on a weapon! (same goes with any kind of damage, elemental/shadow/piercing etc)
Unique Variants on weapons can either be Increased Damage against certain type of monsters (ex. Damage Bonus vs Beast) , Increased Attack Speed, or Charge Time Reduction.
So check what UV you got, and closely to your Ascended, and you will see that the bar is not actually increased!
For the second part, about upgrading it to Levi. Of course do that! When you have an item with UV on, and want to upgrade it you have the option to keep the UV on!
So if you got an "Attack Speed Increased Medium" Ascended Calibur you will craft an "Attack Speed Increased Medium" Leviathatn Blade!
You wont lose the UV when you upgrade it, unless you choose to do so.
See for yourself, the wiki has damage tables for both weapons:
http://wiki.spiralknights.com/Ascended_Calibur#Damage
http://wiki.spiralknights.com/Leviathan_Blade#Damage
Not sure I understand the UV question, but when you upgrade a weapon you have the option of keeping the UV. So if you have an Ascended Calibur with a UV then you can upgrade it to Leviathan and it'll keep exactly the same UV.