How to Overhaul
When your unit reaches a certain level, find Unit Overhaul Technician on the Steel Warship. Everytime after the unit is overhauled, your potency will be increased by 1. And after your unit is overhauled for certain times, you'll get Potency Module and EXP Module as rewards.

After overhaul, your unit level will be degraded to level 1 and unit potency will be decreased to 1. But other attributes will not be changed. You still can equip the higher level gears and your ARM's level will be kept. Each unit can be pverhauled for 100 times at most.
Here is an example:
If your unit is at level 170, your ARM is at level 165 and total potency is 1368, then after unit overhaul, your unit level will be degraded to 1, your ARM will still be level 165 and your taotal potency will be: 1368 - (170 - 1) + 1 = 1200.

Restoration

The overhauled unit can still level up in normal ways. But after it reaches a certain level, it will be restored to the unit level when it was overhauled.
Here is an example:
If your unit was overhauled at level 170. When your unit reaches level 130 again, it will be restored to level 170 instantly. But keep in mind that before restoration, you can not claim your apprentice's EXP contributions.

EXP Recorder

Before restoration, the effect of the EXP Recorder will be 12 times that of before.
There are 3 kinds of EXP Recorders: EXP Module, Major EXP Recorder and Energy EXP Recorder. You can buy the EXP Module and Major EXP Recorder in the Zero Points Mall. But for the Energy EXP Recorder, you can get it only by lottery and Squad Battle.

Modules

Module is the extra bonus of unit overhaul. There are 2 types of module: Potency Module and EXP Module, both of which have 3 attributes: level, CAP and Bonus. Potency Module is for potency bonus while EXP Module is for EXP bonus. If the module's CAP is upgraded, its bonus effect will be greater. Moreover, modules can't be traded or discarded.

Module Level

As your unit levels up, the module will be leveled up, too. Your maximum module CAP is determined by the module level.

Modules CAP

In the R & D Center, you can upgrade module's CAP by using cores, meteors and crystals. As mentioned above, after the module's CAP is upgraded, its bonus effect will be greater. Put in the needed materials, when the upgrade progress reaches 100%, click CAP Up.

Materials for Potency Module CAP

Materials for EXP Module CAP