Activate Com Port 1

​ I have an Inspiron 2650 running Win XP. I want to connect an embroidery machine with serial connection. I have a Belkin usb adapter, but when I try to use the machine I get a message that com port is in use. When I look at modem in device manager, I see that modem is on com 4 and com 2 and 3 are in use. How do I disconnect the modem find out what is on com 2 & 3, and free up the com ports so com 1 becomes available? ​