This thread is resolved. Here is a description of the problem and solution.
Problem: Change one language to another
Solution: There is no option that allows changing one language to another directly. A possible workaround would be to create a new language, duplicate all the content in batch form the main language and then set default language to a newly created language.
This is the technical support forum for WPML - the multilingual WordPress plugin.
Everyone can read, but only WPML clients can post here. WPML team is replying on the forum 6 days per week, 22 hours per day.