To subscribe, please go to your profile,
click "Edit Profile"
click "Upgrade to Premium"  --> get premium

you can chose between different payment methods
and you can chose whether you would like to subscribe
for one month or for one year.

The Benefits of a Premium membership are:

Unlimited play in all games
Instant game access (no ads)
Full screen mode
Enter full rooms
Tournaments
Player avatar (upload a picture)
More chat and game settings
Permanent mute
Permanent buddies