The Preview For Developers GDR1 update can't be installed on the Lumia 530 due to low internal storage. Apparently GDR1 contains an update that will allow future updates to be installed by using the SD card, but this can't be completed on the 530 as it's not running GDR1.
I have tried many times to get it to install, it always downloads the update, but then fails to install it (tried after a reset, all apps uninstalled (for max free space). The max free space available is only 1.3GB on an unlocked version, with all extra apps uninstalled. It's still not enough space to get the update to install.
Microsoft may send out an extra OTA update prior to the official Denim firmware which may allow the 530 to update from an SD card, but I'm just guessing, it might be that it can only be updated via 'Nokia Software Recovery Tool' once GDR1 is released. Or it might never receive an update, it is after all the most basic windows phone available, updates for basic phones are never guaranteed.