How to get back from DD-WRT to stock Firmware
Maybe you want to go back from DD-WRT to Stock Firmware (and then OpenWRT)? Then you may be lucky that there is a DD-WRT version called "webrevert". You simply install it like an update and after a restart you will be back to the factory default version.
In this example we do this with a TP-Link WR841N(D). Select your router on the DD-WRT website (pay attention to the exact name and hardware version!) and download the version called "webrevert" and unpack it. These "webrevert" versions are not available for any router model. So if you just want to try out DD-WRT make sure your model is supported with this way to go back before you flash your router with DD-WRT for the first time.
Then go to "Administration > Firmware Upgrade in DD-WRT and select this file and flash it.
After a restart you are back on the normal firmware (don't get impatient, it can take ten minutes). The network address may also change. DD-WRT normally uses 192.168.1.1, TP-Link 192.168.0.1. If the router still can't be reached, do a 30/30/30 reset, then it should work.