Sprint Duration

There is nothing to stop you from changing the Sprint duration. But there are a few things to keep in mind:

• The Scrum Guide states that a Sprint has "a time-box of one more or less".
• Changing the Sprint duration has an impact on determining your capacity for work. It's not necessarily a direct relationship - that is, going from a 2 week Sprint to a 4 week Sprint will not necessarily double the work that can be done in a Sprint.
• Sprint Planning plans out work for a Sprint. By changing a Sprint duration, you need to plan more or less work. If you increase the Sprint duration, you will have to have more of the backlog refined than usual. This may require additional time in refinement activities. Have you accounted for the need to refine additional Product Backlog Items before changing the Sprint duration?
• The Sprint Review is held on the cadence of a Sprint. By changing the Sprint duration, you will be meeting with key stakeholders more or less frequently. Are your stakeholders capable of meeting and evaluating your Increments on the proposed cadence? Are you able to accept the risk of going longer between meetings of the key stakeholders and the Scrum Team?
• The Sprint Retrospective is also held on the cadence of a Sprint. Are you prepared to go longer between a detailed inspection of the team's way of working?

Before changing Sprint duration, consider why you want to change the duration. What are the benefits? What are the risks?

...can we change the sprint duration after doing few sprints as part of inspect and adapt.

A revised Sprint length may be an outcome of inspection and adaptation, though its short-term consequence would be to make inspection and adaptation harder.