Open iTunes on your computer. Then click on the tab "File" - "Add file to library". You can also transfer into the program window ringtone by dragging it from a folder on your computer in the appropriate section of the library with the left mouse button.
After downloading the desired ringtone, select it in the application window to listen. Follow the playback time of the song to catch the right cut for installation on ringtone. This period cannot be longer than 38 seconds. Listen to the song and note the start and end of the desired area.
Click on song right click to display the context menu. Select "Information", then click on the Settings tab. Here you can change the duration of the melody by setting the checkboxes next to "Start" and "stop Time". In the appropriate fields, specify the start and end time of the playback of the segment you would like to set as ringtone, and then click OK.
Right click on newly created entry in the iTunes window, which will be your ringtone. In the appeared menu choose "Create a version in AAC format". Now you will have a copy of the tune.
Navigate to the folder where you have kept the original version of the song. Next to it you will see the created ringtone, which will have the extension m4a. This is the file your ringtones the call. Right click on this file and select "Rename". Change the extension of the song from m4a to m4r, and press Enter.
If you do not see the file extension, go to the tab "Tools" - "folder options" - "View" folder of Windows. Remove the tick from "Hide extensions" and then try to change the extension again.
In iTunes, delete the shortened version of the song, and then delete the settings made in the "Information" section of the source tune. After that, move the changed m4r file into the program window.
Connect your iPhone to computer and click on the device icon in the upper right corner of the program. Go to "Sounds" and hit Sync to add ringtones to your phone. After the procedure, you can go to device settings to change the ringtone. The procedure of changing the ringtone is complete.