The Liquid Z6 Plus has a microSD memory card reader. If your personal computer can also read that card type (Most notebooks are so-equipped), you should be able to save music files
If the above-mentioned approaches fail or if you prefer not to buy new accessories, you can always use one of the numerous free '3G Uploader' services available online. A search on Katapulco should retrieve plenty of them. 3G uploaders are simple: Transfer your own ringtones on their web site and they will provide a URL. Navigating to that URL with your Acer Liquid Z6 Plus's browser will download the free ringtone.
More on free ringtones
Here are links to some of the 100% free ringtones (Acer Liquid Z6 Plus-compatible) offered here at MartinsRingtones.com:
Free 'Unclassified' Ringtones Free Tropical Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones