Hello Oppala.
If you are not seeing the "Upload File" link when in a category, then you don't have enough posts to upload to the downloads section. If I remember correctly, the downloads is also restricted until you reach 10 posts.
Not to worry, you'll be there soon enough.
Although you have been a member here since January 2009, head on over here to introduce yourself:
http://www.papermodelers.com/forum/welcome-desk/