When using setenv in csh, do not use =. The syntax is
setenv ENV_VAR value
where ENV_VAR is any environment variable you want to set (i.e. JAVA_HOME, etc.). I've always used set to set the PATH variable in csh. The syntax for set is
set PATH=( . . . )
That said, unsetenv should remove the environment variable from the shell environment completely. If you just want to reset the value, reissue the setenv command with the value you want to use for each environment variable.