Stallion
It depends on which client your running now. If your running v2.4 text all you have to do is delete v2.4's exe file and copy the new client to the same directory v2.4 was in and your ready to go.
If your running the gui client then uninstall it first and then create a folder for the new client and just copy the text client to the folder you created and your ready.
Edit: It's not looking good so far with my P3-500e@620mhz. 45% done and estimating 7:28:46 total time. v2.4 would take 5.5-6hrs at the longest.

Which of course it'll take several days worth of wu's before I can get an accurate idea of what my cpu's are going to do on average. I'll just have to wait and see what setiQ says they're all averaging
Celery300a@375mhz looking ok so far.

6.97hrs
9.66hrs
7:11:10hrs est. at 40% done.
Times with v2.4 averaged 9.19hrs.