You’ll need to add some CSS to the stylesheet for your theme, or your installation in Website → Appearance.
This is untested, but probably something like:
#articleAbstract p {text-align: justify;}
or something like that. But probably even better to add something specifically to that template so only the first paragraph (the actual abstract) gets the styling.
Thank you for your prompt reply. However, I cannot implement it. I currently using OJS 2.4.8.2. The problem is how I can go to HTML editor for editing? It is from Site Setting or Journal Manager?