Hi, Martijn.
What needs to be changed? Do both channels share the same custom fields? My example is going to differ depending on your answer. Are these going to be in the same site?
In general, there are two tables involved:
exp_channel_titles
-and-
exp_channel_data
You’ll need to do an update query (after saving your tables before hand):
update exp_channel_titles set channel_id = 5 where channel_id = 4
update exp_channel_data set channel_id = 5 where channel_id = 4
Where 5 is the new channel_id, and 4 is the old.
NOTE: If you aren’t using the same custom fields, you’re going to run into problems. This only changes the channel_id, not any existing custom field remapping.
Make sense?