only way is to progress thru story mode (or play sandbox) to the moment where you meet sebastian and buy for 500 stone of teleportation to umbra
In Umbra - umbra is basicly black (slave) market
there is option to exchange 3 magic items into 1 and this 1 can have 2 bonuses max
bonuses are for armor: energy, health, armor, strenght, agility, endurance, magic aff,
Weapon: speed, attack
Accessory: fear, obedience, all 4 stats
You can have 2 bonuses max like fear + strenght for example so rolling for proper item with proper mods can take time
if you are using like archmage robe or ninja You can't stack bonuses (+2 magic/+2 agility) in current version
same for weapon Claymore -3 speed cant have speed bonus