There are two ways to install CouchDB on Windows.
This is the simplest way to go.
In some cases you might been asked to reboot Windows to complete installation process, because of using on different Microsoft Visual C++ runtimes by CouchDB.
It’s recommended to uninstall previous CouchDB version before upgrading, especially if the new one is built against different Erlang release. The reason is simple: there may be leftover libraries with alternative or incompatible versions from old Erlang release that may create conflicts, errors and weird crashes.
In this case, make sure you backup of your local.ini config and CouchDB database/index files.