I changed it last week. Maximum 1 minute job and I'm not a handy person!
It's a 2032 so cheap and easy to find.
You don't need even a tool! The metallic part of the key is all you need to open the key.
Just make sure you have the new battery already available, to avoid going out, buying, opening the package withe the old battery out.
Of course you can find instructions on YouTube if you feel like watching one before starting the job.