I assume you mean an old Intel Pentium E6500? Only E6500 I've ever heard of and it's the right frequency.
What you can update to -- and it very likely may not be much -- will depend on what your motherboard is, so you'll have to provide that information. I wouldn't get too hopeful as those Pentiums were entry-level at the time (they're essentially under-$100-at-the-time Core 2 Duos with some of the cached disabled) which means I'd be mildly surprised if you could upgrade to a 95W CPU of that generation. Outside of the possibility of a Core 2 Quad, the platform's old enough that I can't advise you to put any more money into it.