You can follow these steps

1. Go to YOURSITE/sites/all/modules/views/theme
2. Open theme.inc and search for function "theme_views_mini_pager"
3. Copy the entire function.
4. Now go to YOURSITE/sites/all/themes/YOURTHEME
5. Open template.php file or create if you don't have the one.
6. Paste the entire function.
7. Now change the function name to "YOURTHEME_views_mini_pager"
8. In my example I am changing the right and left double arrow ("«" and "»") to a text "previous" and "next". For this just replace the arrows with text.

quoted from  : http://www.zyxware.com/articles/3804/drupal-how-to-theme-the-pager-created-by-drupal-views