Convert .Net Framework 4.6.1 Console App to .Net Core 1.1

I've tried searching but can't find out how to convert a .Net Framework 4.6.1 console application to .Net Core 1.1.  I am using VS2017.  I was able to create a new .Net Core 1.1 console application and copy all of my .cs files and that seems to work.  I was wondering if there was a way to convert the solution directly.  In the properties window for my original 4.6.1 application in VS2017, there is not a .Net Core option for target framework (even though I can create a .Net Core application from scratch).

Thanks!