migrating from one domain to another

I want to migrate from one sub domain and move to a new domain on the same server, shorter name! is there a wp for dummies way of doing so, also have a joomla site I wish to move articles over to wordpress, same question as above, is there a wp for dummies way of doing so, and would consider paying if within reason, just starting and really have no budget to speak of! any help would be greatly appreciated.