Safest way to clear/free-up space on Internal Storage/SD Card
Looking for some assistance please; I'm planning to trade-in my HTC One for an upgrade to a HTC One M8 most probably. Retailer is happy to accept the phone with a custom rom on it, so it saves me the bother of returning fully to stock. Got latest ARHD rom onboard but still S-On and original firmware.
Want to free up as much of the Internal Storage/SD Card as possible before handing it over (we got them with 25Gb available out of the 32Gb didn't we), but afraid to hit factory reset in recovery in case it clears the entire storage including recovery files/partition etc and rom image etc, and therefore wont reboot properly.
What's the cleanest and safest way to maximize available space without losing key data/files please? All thoughts welcomed/gratefully received!