WSUS Name Change

[WMSalam]

Dear Colleagues,

After i changed the WSUS server and placed it onto a new server with a
diffrent name, and althogh of modifying the GPO to point the clients to the
new WSUS, no computers appear on the WSUS but 3 newly installed PCs,while
all our previous 200 PCs seem to be still pointing to the old server, what
should i do to reset that??

Thanks & Regards,
WMSalam