If you have trouble to get e.g. from 3.3.x to 4.x (conda update conda "does not work" to get to the next version) than try it more specific like so:
conda install conda=4.0 (or conda install anaconda=4.0)
https://www.anaconda.com/blog/developer-blog/anaconda-4-release/
You should know what you do, because conda could break due to the forced installation. If you would like to get more flexibility/security you could use pkg-manager like nix(-pkgs) [with nix-shell] / NixOS.