How to change Java version used by TOMCAT?

I have Java 1.6 and Tomcat 5.5 installed on my system.

But Tomcat 5.5 accesses Java 1.5 and hence as the outcome I get the error Bad version number in .class file while executing java code with JSP.

How can I change the Tomcat version to Java 1.6?

UPDATE

I tried changing the JVM that the tomcat5w.exe is pointing to the version 1.6 and now I am out of the Bad version in .class file error. But now, I get the following error.

exception

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:498)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:411)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:308)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:259)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

root cause

java.lang.NullPointerException
myfirst.SearchLink.checkURL(SearchLink.java:20)
org.apache.jsp.Test_jsp._jspService(Test_jsp.java:52)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:308)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:259)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

What might be the root cause?