Step 1: After Download the file, you will need a USB flash drive with at least 1GB of space, Plug that USB into your computer and on the root of the USB make a folder Called PS3, inside the PS3 folder make another folder called UPDATE. This is where you will place the Update file.
Step 2: Take the REBUG_4.46.1_REX_PS3UPDAT.PUP and copy that the the UPDATE folder on the USB. Rename the REBUG_4.46.1_REX_PS3UPDAT.PUP as PS3UPDAT.PUP (Windows 8 or Mac PS3UPDAT) and then plug the USB into your PS3.
Step 3: Under settings go to System Update and go to Update Via Storage Media, Select the 4.46.1 Rebug RE and click OK. Allow the System to run the Update and Reboot and your now running CFW 4.46.1 Rebug CEX REX.
*To install Rebug Tool Box, go to the Game Section on the XMB and load *Install Package Files and then select PS3 HDD and install the Tool Box. To use CEX/DEX settings in tool box change to Rebug Mode and Reboot System.