Hi @Vikasbukhari,
Can you indicate what version of OJS you’re using. Are you able to check your php.ini settings to check what your upload limit is set at? Have a look at this post here: File size error while uploading PDF or Word file - OJS 3.1.0.1 - #4 by Dani - where a user described how they addressed file size upload limits by adjusting the php.ini settings.
-Roger
PKP Team