yes you can upgrade you WinMX easily.
There are two ways to do this.
One is to install the WinMXGroup Patch locted here.http://www.winmxgroup.com/
This will upgrade you to the latest versions of WinMX and install a patch that connects to the new cashes.
If your using a hosts file and would like to stay on that hosts file to connect you can find any upgraded versions of WinMX you would like from clicking on the Archive
button located at the top right corner of this screen. Just Look for WinMX folder, the last version of an official release is the WinMX 3.53. The beta version released is very stable, infact more stable then the 3.53 and is in the Beta Folder called WinMX 3.54 beta 4.
Be sure if your using a hosts file to connect that its the latest most uptodate version you can get also. Hosts files work best for connecting if you have the correct info in them, and this has to be updated regularly.
You can upgrade these by simply replacing the WinMX.exe
in your existing folder and restarting WinMX.