Hi Younus,
Support may have a better answer, but the only place I've know that you can manage file size uploads is in SharePoint Central Administration -> Manage Web Applications -> General Settings and then the maximum file upload size property. However, this affects all sites in that web application and all lists and libraries, meaning you wouldn't be able to upload Composer solutions greater than 5 MB, training PDFs, etc...
It may be possible to use JavaScript to hook into the file binding once selected and check the size. That custom function could be placed on the submit button to prevent a save and route when exceeded.
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Joshua Whitener | Winshuttle Evangelist
Exxon Mobil Corporation | 8326258441
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