A couple of methods:
Download Samsung Kies if you haven't done so already, it's necessary to download this free program onto your computer as it provides USB drivers specific to your device (i.e. charging and data transfer drivers). I wouldn't recommend using it for syncing music to your device as it is extremely slow but ultimately that's for you to decide.
All methods require that your memory or microSD card be installed. A 4 GB card is shipped with all Aces' and may have to be installed through the side door on the device. Keep in mind, by default pictures and some apps are automatically stored on the memory card so it might be a good idea to look into getting a Class 6 or higher 16 or 32 GB microSD card depending on how much music you plan to store on it.
This next method turns your Ace into a mass storage device. This is done by connecting your Ace via USB. On the Ace, swipe from the top of the screen to the bottom to bring up the window-shade menu. You should see an area called Ongoing / USB connected / Select to copy files to/from your computer. Tap this area to continue. Tap Connect storage to PC.Tap OK.
If you're using a Windows based PC, an Autoplay folder will appear. Click on, Open Folder to View Files. This is your microSD cards' storage and for the most part should be empty. Right click and select New and then Folder and call it MyMusic for example. Navigate to where your music is stored on your PC, select all, copy and paste it into your MyMusic folder you just created and now you have music!
The last option, if your laptop or PC has a memory card reader, pop it in, do the same as above to create a music folder, navigate to where your music is stored, you can either drag n drop or cut n paste music to the new music folder on the card. Safely remove the microSD card and install it in your Ace and you've got your music.