There are three ways to install MyEclipse for Spring 8.6 M2.
1. Offline Installer - Download offline installers for Windows, Linux and Mac here.
2. Pulse - Available in IDE category of Pulse
3. Add-on for MyEclipse Pro 8.6 - from MyEclipse Add-ons (Software and Workspace Center --> Dashboard) select MyEclipse for Spring
4. Add-on for STS - Install using ME4S for STS 2.3.2 update site or STS 2.5 update site (NEW for ME4S 8.6.1)

What is the best way to upgrade MyEclipse 7.5 to the latest MyEclipse for Spring version?

Hello,

The best way is to get MyEclipse for Spring as a separate install, either thru the offline installer or Pulse. This won't replace your existing version, but you can open your old workspace in ME4S.

HTH,
Dave

I updated original message to reflect that you can now install ME4S into SpringSource Tool Suite (STS) 2.3.2 and 2.5.

ME4S for STS 2.3.2 update site

ME4S for STS 2.5 update site