According to our description at Removing an Issue from a Sprint:

To remove an issue from the active sprint,

Log in to JIRA.

Click the Agile link's down-arrow in the top navigation bar, then select your preferred board from the resulting dropdown menu.
Your board will be displayed.
Either:
Click Plan, then drag the issue out of the planned sprint and into another sprint or into the backlog.
or:
Click Work, then click the issue key to display the Issue Detail View. Select Remove from Sprint from the cog menu (see screenshot below).
(info) Note that you cannot remove a sub-task from a sprint, as sub-tasks always belong to the same sprint as their parent.

On the Plan mode, dragging and dropping the issue from the active sprint doesn't work. You can only reorder the issues on the active sprint by using the drag and drop.