Is there any way i can do this ?
Yeah, your best bet is to make a backup of your files, database, and deactivate any plugins.
Then upload the 1.6 file set and install. Make SURE that you select the upgrade option though, otherwise you will lose all users, threads, posts, etc.
Here's the myBB information on upgrading:
http://blog.mybb.com/2010/08/03/mybb-1-6-released/
