I upgraded a Mid 2012 MBP to latest macOS High Sierra today. While this is an older model the process went smoothly. The unit was running El Capitan (10.11). It should be noted that the hardware had previously been updated. It was running:
- 16gb RAM
- 500gb Samsung EVO SSD
The SSD drive is a solid investment anyone should make on older Apple hardware. Not only is it a performance boost it also sped up the upgrade process significantly.
The first step in any upgrade is to make sure you have a backup. Whether that is a disk clone, time machine or other third party application (like BackBlaze)