Now am using substance look and feel version 5.3.I want to upgrade the it to latest version 7.2.1. I need to know what is the new features in new version and difference between 5.3 and 7.2.1.why we need to prefer the new version.
usually, you take a new version for the improved code, the new functionalities, ...
considering the fact you've missed two major releases already, I would assume the differences between what you are using and what's new is substantial.
'Why we need to prefer the new version'
You don't "need" to do anything. This is pretty much choice based.
Java 5 is no longer supported, so it has critical security bugs that have not been fixed. Java 7 is also approaching end of life. The only way to get all the latest security fixes is to go to the current version, which is Java 8.
Java 6 and 7 contained many language enhancements, and Java 8 has very important new features. See the release notes on Oracle' s site for details.
@JamesCherrill: I am fairly certain the OP as referring to the version numbers for the Substance LAF framework, not Java itself.
That having been said, I doubt anyone here knows anything of Substance (pun intended). You might want to, I dunno, read the documentation? RTFM is always the first thing to try doing in these cases, really.