There are item power thresholds which determine affix roll ranges, and in a lot of cases we can manipulate this by using Blacksmith upgrades for “rerolls”.
For example you have a pair of gloves with +1 to Upheaval with item power very close to +2 threshold, then upgrading them pass the threshold will cause the affix to reroll within the new range and possibly become +2 to Upheaval instead.
Beware this can sometimes downgrade the affixes, so always check the affixes before you upgrade at Blacksmith.