Locate the battery connector and note the orientation of the red and black leads. You will need to connect the new battery in the same orientation.

Gently disconnect the battery from the terminal. A spudger is helpful.

Carefully remove the disconnected battery from the housing. The battery is glued to the housing. Take care to avoid damaging connections in the small wire underneath the battery. In my headset this wire glued to the battery. Use the spudger to gently pry the wire and battery apart, if necessary.

Take this opportunity to measure and record your battery dimensions and specs. You must replace with a battery that fits into the available space.

Properly dispose of the spent battery.