Pretty sure you can't.
Sony, thanks to a lot of complaining from people who care a little too much about it, does not want anyone harvesting. Some people actually pay others for loaded profiles, so that they appear "elite", without doing the work themselves.
Unfortunately, this also punishes those, like yourself who just want to move their own information.
I could be wrong.
I want to create a new account, and I was wondering if it is possible to keep all my saved data, dlc content and trophies from the games I play from my old account. Any info would be greatly appreciated. Thank you!
DLC ownership cannot be transferred between PSN accounts; Trophies are locked to the PSN account who earned them & while gamesave files will work with other accounts, some gamesave files are locked to the user's PSN ID under which it was created.
Your best bet is to create a new XMB User, create a PSN ID under it and not delete the other account. This way you can copy gamesave files from one account to another and see if they all work & still make use of some of your DLCs.