So you've got your ds-x but it still has the older firmware and you want some new pretty skins or just want to get rid of some of the bugs, that's fine. I'll try my best to explain the steps here, should be pretty simple. And if you're unsure which firmware you're running; put your ds-x into the DS, load er up, when the option comes up to choose apps or music, pick the last one on the right with the question mark.
So the first thing you wanna do is back everything up. If you just pulled it out of the box and there isn't anything on it, well, no need to backup. Everything will be deleted once you do this, so do it now. Basically just drag everything off your ds-x and move it into a folder on your desktop.
Now that you've got everything backed up, let's format it. The easiest way is to find the ds-x in windows explorer, right-click and choose format. You will want to use the pulldown menu and select FAT(FAT16) and then click start. Some people suggest using a program called swissknife, you can find more information on their site, here.
Now that it's formatted, we're going to update the firmware. You can download the updated from this link here or visit news.ds-x.com/ and find it there. So download the updater, make sure your ds-x is plugged in and run the .exe file for the updater. It will check your firmware and check to see what the newest firmware is from the ds-x team. Once it's done checking, hit "Update Device" and you're off. It will go through a few things and finally say you're done and up to date and then tell you the changes. Close the updater, eject your ds-x and then reconnect it.
Now you have a fresh updated ds-x. First thing you wanna do is format it again. Better safe than sorry here folks!
Now you need to put the skin files and everything else onto the ds-x. You can download that here or visit the news site as mentioned earlier. Everything will be in a zip folder, so download them and put everything into the root of your ds-x.
Now if you've made it this far without any issues, good! If not, do them again! If you backed up your ds-x with your roms and saves, put them back on now and then safely eject your ds-x and you should be good to go.