Decision on Sprint duration

Hi,

I'm new to Scrum framework and working towards the PSM-I exam.

How and who decides on the duration of a Sprint within the organization at a firm new to Scrum? My firm comes from traditional waterfall methodology and senior management seems deadlocked around -
1. Duration of Release Cycle
2. Duration of the Sprint Cycle

Who should have the final say (which role?) about the durations? Also, will help me with my understanding for the exam.

Regards,
AJ