https://bugs.winehq.org/show_bug.cgi?id=40317
--- Comment #15 from Vincent Povirk madewokherd@gmail.com --- The easiest way is to let Ubuntu's package manager update your Wine package the same as the rest of your system. Any Gecko or Mono updates will be included with the new Wine release.
It is also possible to manually update Mono by downloading and installing the msi, but due to an msi bug you have to be careful to do this using wine64 in 64-bit prefixes, otherwise it can cause problems.