Hi Sunil - Welcome to the Community!
Changing statuses is based on the workflow. If you are on a board, you should be able to drag it to the next available status if it is in another column. If not, then you should be able to go directly to the card and change the status there.
For the "new" JIRA issue view you simply go to the status on the right side, click the drop down and select the transition to the desired status.
If you are in the "old" JIRA view, you should be able to click on the Workflow drop down and select the status.
I hope that helps!
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