how to replace the charger inverter in a four winds

I'm having good success with reconditioned telcom agm batteries.

What make and model is the current inverter/charger?

Inverter-charger should charge the AGM just fine with a change of settings.

If instead there is a far more common converter-charger it would be best to post the model number. Some are great, some adequate, some miserable. Some just need a plug in controller.

No the entire power distribution center does not need to be replaced.

Too many unknowns to give you a specific answer.

Shop for a combination inverter/charger/automatic transfer switch. All of the good quality ones do "smart charging" and have settings for flooded (wet) or AGM lead acid batteries as well as lithium. Better ones actually have an input for a generator.

If you get the combo I suggested, start by removing the old converter. You want your new inverter/charger/automatic transfer switch located as close as possible to your batteries. Wire your DC distribution panel directly to the batteries (via s mega-fuse) and an ampere meter shunt). Your outside cord should go directly to the new unit. The output of the new unit goes to the AC breaker box.