It should just open, but a better process is to create a new project of the same format/frame rate. Quit Media Composer and copy the bins from the older project into the new project. Relaunch, open project and bins as you would usually do.
Should just open, and if you're unsure, create a new project in v8 and copy the v5 bins into it. Do note that 8.6.x has a problem where it often refuses to open bins from earlier versions (error messages appear). 8.5.3 seems to open them fine for me.