Image upload trouble (tried all method)

Hello,
i use wordpress 3.6 on 1and1 hosting, i have put a Lovestory Theme that makes WP look likes a dating website : http://www.sochan-union.fr
but i have issue with photos, when a user is in his account he can upload a photo more than 3MB, and it’s the same via the admin of WP.
I tried a php.ini, wp-config and htacess method, but nothing work and i have tried with my host to makes some test and it’s not his fault.
In my upload window it shows that i can upload up to 8MB…
In my htacess i got :
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

And modifications makes my url rewrite lead to 500 error.
I had succeed in a way with PHP.ini beacause it has modified my uplad but from 8mb to 2mb…
i’m lost, help welcome 🙂
thanks