Welcome ashiq!
As a vector graphics editor, Inkscape will not be able to edit the PNG image, hardly at all (because PNG is a raster format).
Here's some info about the difference between raster and vector graphics (at the top of that article) (written for newbies).
If the image is relatively simple, it might not be very hard to redraw it using Inkscape. Then you'll have a vector file that can be easiliy edited and re-edited with Inkscape. If you can show us the image, we can give you some idea if it can be re-created easily, or maybe give you some other alternatives.
