Ohhh...Please don;t come with that type of $350 proposal.
I managed to do it myself.
there was a file mytheme_recent_posts.php and in that file there was a code---
<img src="<?php bloginfo('template_directory'); ?>/scripts/timthumb.php?src=<?php echo $img ?>&h=250&w=300&zc=0" width="300" height="250" alt="<?php the_title(); ?---
And i changed zc=0 to zc-1 as i required.
That was what i needed.
Thank You .
NB:Now I feel pity of this forum that no one replies promptly to such a silly problem even after many requests from me.And i say sorry if you guys didn't understand my question clearly because i asked you to edit TimThumb which was not actually needed.