You can skip versions when doing LTS-to-LTS upgrades, e.g. you can go from 11.10 to 12.04 LTS, then to 14.04 LTS, and then to 16.04 LTS.
However, this will take a long time, you are probably looking at 3-4 hours minimum there depending on your internet connection and other factors.
Since this is a substantial migration, you should also expect small things here and there to go a bit wrong, so this might mean even more effort to get things going smoothly after you are finished.
As you have hopefully backed up your data like you always should when doing upgrades, the quickest and cleanest way would be to do do a fresh install of 16.04 LTS, you can get away with 20-30 minutes here.
Just as a side note, if you tend to wait this long with upgrading your installations, I'd suggest to stick with LTS releases.