My MacBook Pro says replace battery soon

MacBook Pro (Retina, 15-inch, Early 2013), 2.4 GHz Intel Core i7, 8 GB 1600 MHz DDR3,

NVIDIA GeForce GT 650M 1024 MB, Intel HD Graphics 4000 1536 MB

MacOS High Sierra version 10.13.4 (17E199)

In my system preferences I have a message that says replace battery soon. How much time do I have to do this and where do I get a replacement battery and how much does it cost? Do I have to take it to an Apple store?

I have had problems with my MBP shutting down while I'm using it with battery at 100%. Sometimes the bottom is very warm eventhough it is sitting on a table with nothing around it.

Also I think my speaker is busted because there is a buzzing sound if I play music or video. Is that replaceable?

Thanks in advance