To remove the battery, remove the spade connectors. Avoid shorting out or touching the terminals. Dispose of the expired battery according to local regulations. It will still contain charge so handle with care - tape over the terminals if neccessary. This photo shows the new battery.

To attach the new battery reconnect the leads, noting red lead goes to red terminal. I made a mistake here and reinserted the battery back to front but it still works. It's a rather heavy and clumsy component.