For relieving the spring pressure many have a 3/8 square drive cut into them. To remove the tensioner its in the center of the unit, the pulley on the tensioner will have a fastener too might not look like a bolt hex head it can be a torx head Dodge likes to change things up for laughs.
Most pulleys have a cap, so that has to be removed, then you can see what tool you need to remove.
Search Dodge Neon Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Dodge Neon Experts