For this achievement, simply max out any skill/power for one of Shepherd's abilities. In the "Squad" menu when you hit start, you can allocate skill points for your characters, which are earned as you level up. Once any of Shepherd's skills are fully leveled (requires 10 total skill points), you will be asked to "evolve" your skill. This means choosing between an offensive and defensive final version of the skill. Once you make your choice, the achievement will unlock.
It's rather difficult not to get this achievement in a playthrough, but a solid way to get the achievement later in the game if you haven't already is to use the Tactical Shift upgrade. This upgrade allows you to wipe Shepard's skill points clean and redistribute them however you like. Make a save file, use the upgrade, and redo Shephard's skills, making sure to max out and evolve at least one of them. Once the achievement pops, load your save to return to your Shephard build.