To move and copy articles in Joomla 2.5 you have to use a batch process of them. Starting in your article manager, Main Menu -> Content -> Article Manager.
Head down to the bottom of your articles to the section called, batch process. This section allows you to batch process access levels, languages, and change category or copy articles in batch.
To move articles simply select the articles you wish to move, by selecting the checkboxes on the left. Then head to the bottom and select the category you wish to move them into by using the dropdown.
Ensure that the “Move” option is selected and click the “Process” button.
Your articles will now be moved.
The same goes for copying articles, just follow the same process but ensure that the “Copy” option is selected.