More info please. Do you mean your friend is actually living at your house and you're ready for them to move on? Or someone who comes to visit and you're ready for them to leave but they keep hanging around?
I agree with kimkay, there's different ways to handle unwanted guests from unwanted visitors. If someone's been living or staying with you and you want them gone you may have to take them to court. Yes, I'm serious!! My daughter found this out the hard way when she had opened her home to a homeless friend to stay until they got on their feet, the friend became unruly one night so she "threw them out". Later she received notice she was being sued by the person for unlawful eviction!! That person won the lawsuit!
If it is someone merely visiting, ask them to leave. If they refuse, call the police.
The best way to get such a person out of your house is to be sincere to yourself and have a one on one session with him or her. Open up without emotions, just be straight forward and enumerate all the difficulties you are facing as a result of hosting him or her. I know it is such a difficult task but you can try. If you feel you are not bold enough, you can approach someone mature to do this on you behalf.