Go to any viewport. Clicking on the name of that view port drops down a list of possible views .
Select image clip viewer for the viewport. Select import and navagate to your image sequence.
once imported you can than use the export function listed in the same area as import. Name your
export and chose among the many formats available under the file type cell.

The same can be done in the flipbook which can be lauched under the animation menu for example.
Hoe this helps.