Then I guess, there is a HTC's promotion for all of HTC One X/S/V smartphone. That's great !!!!
Before backup & wiped the current ROM, I download & install the new PrimoS - 1.0 Beta ROM (you can Download & install this ROM from XDA forum here with own risk).

Good news: There is the other method for us to upgrade your Dropbox upto 23 GB:
1. As first, you need to download this apk file on your smartphone
2. Install it, then you can see this messenge :“Continue to Dropbox!” as picture below:
3. Choose "Next" to continue and you can sign in your Dropbox account. And you can see your Dropbox capacity will be upgraded upto over 23 GB
Thanks Theos0o from XDA Developers forum for your apk file !!! Enjoy it (as your own risk :D)