2006 Dodge Dakota SLT. Engine Size : 3.7L v6.
Question: how hard is it to change a valve or a spring in a 2006 dodge Dakota motor?

Answer: Well, to be general about your question, changing a valve spring and changing a valve are two different repairs. A valve spring can be changed with the correct tools with the cylinder head still on the engine. A valve on the other hand can only be replaced by removing the cylinder head. That is a very big job.