You can easily add a label to a company by clicking on the label icon on the company page and choosing from the existing labels.
The chosen labels for the company will appear besides the company name and will have a tick in the colour swatch next to that label.
To remove a label just click the one you want to take away. You will see that the tick in the colour swatch next to the label disappear and that the label does not show besides the company name anymore.
The labels applied/removed will auto save. Just click elsewhere on the screen to close the label options when you are done.
To learn more about creating a label read our FAQ How do I create a Label.