In Diablo 4, even though you can find the rarest items, imbue them with ideal aspects, and add the best gems, sometimes this is not enough to complete your build. More precisely, the problem may lie in more fundamental aspects, namely its statistics. 

Excellent affixes that are not suitable for your build can cause you to get rid of Diablo 4 Items that took tens of hours to obtain. Fortunately, players who have reached at least level 25 in Diablo 4 can reroll item stats by spending money and some rarer materials. This mechanic is based on RNG, requires a lot of investment, and will be indispensable in the late-game stages. Here's how to do so.

In Diablo 4, the Occultist NPC is responsible for rerolling item stats. Here are step-by-step instructions on how to change your item stats:

    Reach at least level 25 or get the Codex of Power Aspect to unlock the Occultist, and then find him in one of the big cities.
    Talk to the NPC and go to the rightmost tab with the image of a sword against the background of a magic circle.
    Place any Rare or Legendary item into the empty slot.
    Now, you can choose one of three affixes of your item that you want to reroll. 
    By selecting the stat you want to reroll and confirming the transaction, you can choose one of three alternative stats from the list you saw earlier. Now, you can choose what you want or refuse all options and leave the old affix if none of the proposed ones suits you.

By the way, affixes on items are being reduced to more potent ones for Diablo 4 Season 4, with legendary items holding three affixes and rare items holding two. 

It is worth noting several essential points regarding this reroll. Firstly, the cost of reroll stats is relatively high and, in addition to gold, can include rare items like Fiend Roses and Forgotten Souls. Money and items spent on rerolling will disappear regardless of whether you take a new affix or leave the original one. Fortunately, this system has no restrictions on the number of rerolls, so you can try as many times as you like.

That's all you need to know about rerolling item stats in Diablo 4. Of course, this is not a cheap thing, since finding the ideal affixes among a huge list is not easy. But this is another good way to power up your build late in the game.