You should see that the battery is connected by 2 wires, one black and one red that lead to the logic board.

Make note of what color wire is soldered to the respective node before un-soldering the wires.

Heat up a soldering iron and melt the solder that is connecting the battery to the logic board.

Use a solder sucker to remove the solder as it melts, using caution to remove the wire.

Completely remove the battery from the device.

Insert the new battery and re-solder the corresponding wires to their respective locations.