How to Display full post for archive or Tag of post?

Hi my site is

http://financefire.com/

i am using free priimo theme of them dezineappz.com

When a user clicks on a tag or category on my blog then it shows only summery of the post with a read more button.You can check it:

http://financefire.com/tag/best-companies-to-invest-in-2013

But i want to show the full text in tag of each post my blog.Can any one tell me please how can i do this in this theme?

One of my friend told me to edit archive.php file but i do not find any archive.php file from edit theme option.So what can i do?

Thanks

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