If you use the Linksys WRT54GL router it is really easy to switch between the different available firmware versions.

No special process is necessary like on other routers!

From Stock to DD-WRT

First, download and install the correct mini firmware for your router by using the WebGui. After that, install a firmware of your choice like the std or vpn one.

The files can be found here:

https://www.dd-wrt.com/site/support/router-database

or directly here: https://www.dd-wrt.com/routerdb/de/download/Linksys/WRT54GL/1.0/1.1/dd-wrt.v24_mini_generic.bin/1961

and here: https://www.dd-wrt.com/routerdb/de/download/Linksys/WRT54GL/1.0/1.1/dd-wrt.v24_std_generic.bin/1963

From DD-WRT to Stock

If you want to go from a DD-WRT firmware to the original stock one this can be done also very easily by also using the WebGui of DD-WRT.

The newest one for the WRT54GL router can be found here: http://www.linksys.com/us/support-article?articleNum=148652

or directly here (24.05.2016): http://cache-www.belkin.com/support/dl/FW_WRT54GL_4.30.18.006_US_20160108.bin

From Stock to OpenWRT

If you want to switch from the original firmware to OpenWRT you can also use the WebGUI of your stock firmware.

From DD-WRT to OpenWRT

1 step) From DD-WRT to Stock

2 step) From Stock to OpenWRT