The Internet Corporation for Assigned Names and Numbers (ICANN) has a Uniform Domain Name Dispute Resolution Policy (UDRP) which defines how to resolve trademark-based disputes over domain names. In accordance with the UDRP, you can dispute a claim to a domain name by following ICANN's Uniform Domain Name Disputes Resolution Policy.
The UDRP does not apply to country-code top-level domains names (ccTLDs), except in a few cases where the local administrator has decided to adopt it.