Ways to reduce ram use:
* Tip: Purge the Downloads Queue! (click on blue link)
* And reduce shared files if over 2,000
* Disable Ultrapeer capabilities under Advanced options > Performance. Perhaps the other options on that window too.
* Close LW periodically.
* Check your version of Java .. some versions may be less ram efficient or work better on your system.
* Close off searches you finished with.
* Set uploads & downloads to auto clear after completion.

But 512 MB ram nowadays is a little small.