There are lots of free tools you can use to turn an image into black and white. The following are some of these tools with instructions on how to use them.
Clicking Edit will let you upload an image to the site. Go to Basic Effects > Colors, and decrease Saturation all the way down to the left. Apply and Save.
Open Pixlr Editor. You will have an option where will be your image coming from. Go to Adjustment > Hue/Saturation, and decrease Saturation down to -100. You can also get the same effect by going to Adjustment > Desaturate. File > Save to save it.
GIMP (free software)
Open an image. Go to Colors > Hue/Saturation and move Saturation level down to the left. Save your file.