You can find any lord with the Westerlands and ask to "Make Peace." They will give you an amount of money you can pay, and then you relations should go back to zero. As for improving relations, it is usually things like aiding the caravans/lords/peasants/patrols in fights against their enemies, or releasing lords from captivity (which you can usually sneak into the castle anyway to do something like that.)

The key with madmatthatter's recommendation is to spot a Westerland's lord that doesn't aggressively start to pursue you. There will often be housed in a lanister town or castle.

The ones that chase you will tend to just insist on attacking you anyway.

I suppose my issue is I can't find any westerland men that don't want to kill me on sight. I found a way though. I joined the vale who went to war with the lannisters, once peace was made they became passove of me. Relationships are still low but I'm not attacked on sight anymore.

Another suggestion for you in future. the best way to make peace by talking with an enemy lord, is to look for a lord that is in a castle/town, go there and approach the gates and then ask to speak with a lord. They won't be hostile then