Generally you want to establish a cadence and keep the sprint duration the same but, there a lots of good reasons to change sprint duration after the project has started. Some common reasons are:
-Sprints that are too long become a planning nightmare
-Sprints that are too long don't deliver features in a timely manner for customer feedback
-Sprints that are too short don't align with story work complexity
-Sprints that are too short don't allow enough room for improving product quality and sustainability (tech-debt, refactoring, etc).
Changing sprint duration may seem scary at first but if you consider all the stakeholders in the equation you will identify what processes and people are impacted with a change. Common impacts include activities around release planning, documentation, and customer-feature communication as well as your planning/review/retro.
Generally moving to a shorter release will tighten the feedback loop on your scrum team and force continuous planning behaviors that often are neglected when sprints become too long because teams/pm's believe adding more time to a sprint duration will address the uncertainty factor in delivering within a sprint.