which old windows folders? - the 'Windows.old' ones?
You can use Disk Cleanup to get rid of them - check the advanced options.
Which Java varsion do you have installed? - make sure it's the latest one by visiting www.java.com
and comparing the version offered with the version quoted in your Programs listing (and you should never really install Java until your system is up-to-date on everything else - it's currently a major source of infections.)
Unless you actually use Java applications, the current recommendations are to uninstall it completely, because there are known unpatched vulnerabilities which Oravcle shows no signs of hurrying patches for.
Yes, by all means, do the rename - it may well help. (just test Windows Updates first, in case the cleanup has solved the problem!)