To transfer out a .BE domain you're going to need an authcode. Different from other ccTLD's, the authcode for .BE domains can be requested by/for the registrant through the DNS Belgium website. Enclosed in the registry WHOIS-tool there is an option to send the authcode. The authcode will always be sent to the registrant e-mail address.
Once the authcode is received, inform with the gaining registrar/provider to initiate the transfer from their end and supply them with the authcode.
- Take note: an authcode can only be generated a maximum of four times. Then it's restricted for a time period of 7 days before the authcode can be requested again.