Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for chest pain, severe breathing difficulty, fainting, or a suddenly cold, pale or blue hand.
Seek prompt medical advice for increasing redness, warmth or drainage; fever; worsening pain after initial improvement; an opening wound; new hand weakness; or persistent numbness.
Contact the surgical team urgently if the elbow changes shape, you hear or feel a snap, or the joint becomes unstable after an injury.
The article also says
Contact the surgical team about wound care, exercises, medicine side effects, persistent swelling or returning to activities.
Every sign above is quoted from the sofidex article on Elbow replacement. If you are not sure, err upward — it is always reasonable to be checked.