I attach Brutalizer to a unit, it gets +1 from Brutalizer and +2 because of Brutalizer effect. If I detach Brutalizer from the unit, does the unit keep the +2? If I reattach the equipment to the unit, does it get +2 again and push the equipment to 5 might?

No, the unit does not keep the +2 bonus when Brutalizer is detached.

According to the rules and the specific interaction for Brutalizer:

1. Detachment: When Brutalizer detaches from a unit, the unit immediately loses all bonuses provided by that equipment (both the base +1 Might and the conditional +2 Might). The unit returns to its base Might.
2. Re-attachment: If you re-attach Brutalizer to the unit, it will gain the bonuses again. If the unit had 2 base Might, it would gain the +1 (base bonus) and the +2 (conditional effect), totaling 5 Might.

As noted in the rules for attachments (Rule 136.3.a), the Might bonus is applied only while the card is attached and stops applying as soon as the card is no longer attached.