Buy Snow Leopard for 20.00. Backup hard drive on external. Wipe Mac hard drive and install SL with disk. Download Mavericks and you have a computer with more speed and life.
Once you have your stuff on a hard drive I could walk you through the rest if you needed to. Or you follow this.
http://www.macworld.com/article/2056564/how-to-install-mavericks-over-leopard.html