The upgrade path is now open. LMDE 1 “Debian” users can upgrade to LMDE 2 “Betsy” by following this tutorial:
As always, make sure to read everything and don’t hesitate to connect to the IRC while performing the upgrade.
One important note among the warnings: Make sure to disable Romeo prior to upgrading. Cinnamon 2.6 and MATE 1.10 will hit it very soon, they’re not fully stable yet. If you want to test them, it’s better to enable Romeo post-upgrade so they don’t interfere with the upgrade.