Hi all,
Can i reduce the datafile size to 2MB ?

What database are we talking about? Oracle, Informix?

If it is Oracle then you should be able to do it on the condition that you have no Oracle blocks in use above the 2Gb limit (HWM: high water mark). If that is the case you are facing a more difficult path because you have to figure out which object (tables, indexes etc) are using those blocks and how to get them out of there.

You can try coalescing the objects in the tablespace, exporting, dropping or recreating them with proper storage parameters. But if your datafile usage is already pretty high, you might not be able to drop below the HWM at all.