I was going to go from SMF to XF1, but a plugin I wanted to use and the theme I have chosen have both been updated to XF2, so I figured I might as well just go to the latest version.
XF2 doesn't have a SMF 2.x importer built into it. XF1 does, however. So you'd need to do a two-step import. SMF 2.x -> XF1, and then upgrade into XF2. You can access the importers from Admin CP -> Tools.
The manual for importing is located at: https://xenforo.com/help/importing/. Combined with the notes on the importer page you should be able to complete an import into XF1 with your SMF data, and then upgrade into XF2 after confirming the data was moved in properly.
I'd use a clone of your forum and run a test import locally first and see how it goes.