You only have to make a copy of your project folder. For example, i got a project name Something, inside C:\Users\UserName\Documents\UnrealProjects, all i need to do is thrown the entire project Something into another folder or a zip file, then put it into somewhere safe. Beware that even though my project is a pretty small one, it still take around 1gb to 2gb. You can keep several version of the same project in different folder at the same time too.