Most places will let you exchange your ring within the first 30 days for free. After that, they may not do an exchange for you, or if they do, they might charge a fee. Tungsten Rings can not be resized, so make sure you purchase a ring from a company you know will do an exchange for you so you do not have to purchase a new ring.
Also, make sure you know what you are getting into about the fee to make an exchange. Some places, like Tungsten Fashions.com will do an exchange for free for the first 30 days and after that they only charge $7.99. Many other companies will charge as much as $75.00 to do an exchange, so do you due diligence and call the company or find out the exact fee.
Tungsten rings are great, just make sure you know what do to if you happen to gain a few pounds - or better yet, lose a few!