EDITED: looks like this not works
Go to C:\Program Files (x86)\Rockstar Games\Grand Theft Auto IV\IVMP
Find settings file, right click and open with notepad
you will get this
<settings>
<ip>95.141.37.186</ip>
<port>7173</port>
<nick>Name</nick>
<pass></pass>
<windowed>0</windowed>
<fps>0</fps>
<chatfont>tahoma-bold</chatfont>
<chatsize>10</chatsize>
<chatbga>0</chatbga>
<chatbgr>0</chatbgr>
<chatbgg>0</chatbgg>
<chatbgb>0</chatbgb>
<disableie9fix>0</disableie9fix>
</settings>
add the 4 in the port and save file and replace it