Problem site and admin section broken!! HELP

Hello,

I run a local government based site for young people i was browsing themes as thought i could do with a change, i activated a theme that i thought looked cool and (other than wishing i hadnt) i keep getting this message:

Fatal error: Cannot redeclare is_valid_url() (previously declared in /home/armanwad/public_html/activeyouth.co.uk/wp-content/plugins/wp-to-twitter/functions.php:19) in /home/armanwad/public_html/activeyouth.co.uk/wp-content/themes/polaroids/functions.php on line 275

The message appear when i try to log into the admin section, and the site itself, i dont know what to do? i cannot fix anything as i have no access, can anyone help? I really hope someone can 🙁