How do you install a 165x76SEMAtensioning spring on a Murray riding mower

Not sure which spring you mean, as there are a few, but this series of videos pretty much covers all the repairs you may encounter*.

165x76sematensioning spring on a murray riding mower - Bing video

Let me know if they help.

*Don't let the different makes/models shown throw you as the process and procedure are fundamentally the same.