When you conserve something, you do not wish to waste or deplete any of the available resources. You attempt not to change anything drastically. example: During the summer, theater owners conserve energy by switching off the AC. The Minister asked the people in cities to conserve water. Preserve, on the other hand, suggests that you make attempts to keep something as it is, without making any changes. In other words, when you preserve something you keep it intact. You keep it safe, protecting it from danger. ex: Our government doesn't do a good job of preserving our monuments. This is a beautiful old house. We must preserve it. link for help: http://www.english-for-students.com/Difference-between-preserve-and-conserve.html

Great answer from 'Michelle' but additional note. Sometimes 'preserve' applies to when you are restoring something to a historical state. A person could 'preserve the historical district' which may mean actually repairing or rebuilding to a historical state.