RubyInstaller-2.5.0-1 brings some new features and makes the switch to OpenSSL-1.1.0. See the ruby-2.5.0 release post and the the RubyInstaller CHANGELOG for more details. Please note, that many gems are not yet compatible with Ruby-2.5 on Windows.
You should therefore stay on 2.4.3 until it’s better supported, unless you want to actively contribute to fix these issues. One way to support ruby-2.5 is to update to the just released rake-compiler-dock version 0.6.2.
All binaries are available in the Download section!
A previous RubyInstaller-2.4.x installation should not be updated by installing RubyInstaller-2.5.x into the same directory. This is because gems with C extensions are not compatible between ruby-2.4 and 2.5. It’s best to use a new directory for 2.5.x.