assuming, as you said, that you are running phpbb 3.1.9;
1. download the zip file from the link above.
2. unzip it on your computer
3. using your ftp, upload the resultant folder named redgrand to your server to the phpbb folder named styles
4. in your phpbb admin panel, click on the customize tab
5. click on install styles from the left menu
6. you will see the redgrand style listed, click on the link that says install style
7. go to the main page of the admin panel, click on board settings in the left menu.
8. scroll down and choose red grand as the default and as the guest style
9. click yes for override user
10. back to the main admin panel page, click on the button that says purge cache and then click yes.
11. go back to your main board home page, on your keyboard, hold down the shift key and click on the reload/refresh button in your browser.
remember, nothing about phpbb 3.0 works with phpbb 3.1
not the files, not the MODs, not the styles, automod does not work etc. etc.
I'm baaaaaccckkkk. still doing work on donation basis. PM your needs.
Premium phpBB 3.2 Styles
If a tree falls in the forest and nobody is there, does it make a sound?