usually after gaining admin acess on wordpress website we upload shell on website, its takes some extra time, even you can deface wordpress's index page without uploading shell !
Goto wordpress dashboard than theme editor and you'll see 2-3 thmes there like twenty ten and twenly eleven.
Look there for active Theme on That website and edit index.php of that theme. and you'll see your deface pages on website's home Page.
Bypassing Permission Denided for index.php in wordpress
sometimes after upload shell on wordpress website when you'll try to replace index.php's socurce code in public_html/ directory with you deface page, it will show error like permission denided, can't write in file etc, and sometimes permission change dones't work, then follow the same method whic is give above, change active theme's index.php file and home will chnage with your deface page.