Sorry I was not clear enough to explain the issue. To print multiple parts at the same time:
Option1: load stl files in UP Studio and save them into a single tsk file. In this case, all parts print with the same print paremeters. You will able to reprint it from touchscreen history list.
Option2: created tsk files individually and load them into UP Studio, while connected to printer, click print. In this case the print parameters could be different for each tsk files. However in the touchscreen history the print job will be break down into invdividual tsk files and user cannot reprint the whole job again.
Currently multiple task files cannot be merged into a single file, so option 2 is the only way to print multiple existing tsk files.