First of all, you should check the camera's settings. Most likely you will be able to set the camera to save the files as JPG instead of Raw (cr2).
In some cameras, you can also choose to save both JPG and RAW files.
If you don't know what Raw files are and don't use the advantages of those files, I would rather set the camera to ONLY save the JPG file, since cr2 files are considerably bigger, which means you would be able to save more pictures on the card you are currently using.
.cr2 files are Raw images produced, among others, by Canon cameras.
You can use the software that came with the camera to convert those images to JPG, or if you don't have that software anymore, there are image processing software that will be able to convert cr2 to jpg.
Of course, Facebook, won't allow uploading cr2 files.
More about Raw Images on Wikipedia
If you don't have any software capable of converting Raw files to Jpg, there are also websites offering online converting, for example this one here: Raw Pics.io
This video here will explain how to set the camera for file type and quality.