When I try to run an app on my iPhone via Xcode, it shows an older version then what I am working on - I have changed images and layouts etc.
How do I clear a cache or something just for dev apps?
This hasn't happened to me before. With the simulator it's easy to reset it:-)
Delete you app and everything from it's bundle (.app, documents, cache, etc.) will be removed.
If you have an outdated view layout - it's better to check the source-code, the most likely you are launching an outdated version.