Air carrier First Officer reported a terrain warning during approach. Flight executed a go around and returned for landing.

Narrative

While on final for Runway 23 I was flying the visual for Runway 23 and had the ILS 23 loaded in the FMS as a backup. We were cleared for the visual 23 and was told by Approach to contact Tower; which the pilot monitoring did. I noticed I was below the glide slope and disconnected the Autopilot; I believe we were at around 3500-4000MSL when I engaged the Autopilot disconnect button. At about the same time that I disconnected the Autopilot we received terrain aural warning. I immediately went into max thrust and initiated a go around. In the climb for the go around the Captain; who was the pilot monitoring took control of the aircraft and we switched roles. I began duties as pilot monitoring and begin communicating with the Tower who instructed us on vectors and altitude to climb to. Tower told us to contact Approach to be vectored back around to attempt a landing onto Runway 23 again. We then landed without any further incident.Cause: I believe the root cause was not catching the descent below 4000 timely enough and not actively ensuring that I remained above the glide slope in all phases of the approach to final. Had I remained above 4000msl I believe I could have avoided the terrain alert.Suggestion: To remain at or above the glide slope when approaching to land in areas with hilly and or mountainous terrain. I will in the future request an ILS approach when available even when a visual approach may be offered as to ensure terrain clearance is adequate along the flight path.