I know there is a tutorial already on PSPGEN but the downloads require registration and all. I wasn't able to register with some errors. So I made this tutorial with download links, so that it is easy. DO NOT CONTINUE IF YOU DON'T WHAT YOU ARE DOING!
For those wanting to downgrade, here is a tutorial with the things you need.
Before starting you must have all this ->
1) Of course a PSP with 6.20 TN-B/C (HEN)
2) PSPident 0.6
3) PSAR Dumper for 6.00 - 6.20
4) 5.00 Official EBOOT
5) 5.03 Official EBOOT
6) ChickHEN R2 Tiff HEN
7) ChickHEN R2 Signed EBOOT which runs directly from XMB > GAME
Now you are ready to go!
Note before you start :
1) Formatting Memory Stick and Restoring Default Settings is not necessary but you can still do it.
2) You need not change the Flash0 protection. Let it be enabled.
-First use PSPident to know whether your PSP is a 2g, 3g or a 4g module. [2g = PSP 2000 (Downgradable), 3g = PSP 3000 (Downgradable) and 4g = PSP 3000 (Non Downgradable)]
-You will see your motherboard info, in that you must have Motherboard Type : Either Slim (02g) / Brite (03g) CONTINUE ONLY IF YOU HAVE A 2G (PSP 2000) or 3G MODULE (PSP 3000)
-Place the 5.00 Official EBOOT on the root of your Memory Stick and the PSAR Dumper application onto PSP/GAME.
-Now launch the PSAR Dumper from GAME menu.
-Press ? and wait for a while till it decrypts the stuff for you.(You will see rapidly appearing lines when you press ?)
-As soon as the decryption is done, you will be able to exit by pressing x.
-Now you are back onto the XMB.
-Now connect your PSP to the PC and you will see that a folder named F0 is made by the PSAR Dumper onto the root of your Memory Stick.
-Now make a folder called seplugins on the root of your memory stick if you haven't made it already.
-Now copy the version.txt which can be found in F0>vsh>etc>version.txt and paste it into the seplugins folder that you just made.
-Ones done open the VSH Menu and select Restart VSH. (For 6.20 TN-B users, you need to enable the FAKE INDEX.DAT in VSH Menu before Restarting VSH and for 6.20 TN-C users the FAKE INDEX.DAT option is not visible in VSH menu but is already active, so just Restart VSH)
-Connect PSP to PC and place the 5.03 Official EBOOT onto PSP/GAME/UPDATE/EBOOT.PBP i.e make a folder named UPDATE and put the EBOOT.PBP of 5.03 Official EBOOT into the UPDATE folder. Then, place the UPDATE folder onto PSP/GAME.
-Disconnect PSP and then start the update from your PSP > GAME menu.
-The thing will start without any problems if you haven't made any mistake.
-After the installation is done, you will get a blue screen with some lines written. On that screen just press o and then your PSP will start again.
-These were the steps followed by me and voila!
-Tips -> Never Update Your PSP if you are enjoying a CFW / HEN with more compatibility.
-> Use the ChickHEN R2 Tiff to get your PSP into the HEN mode. Keep trying until it happens.
-> Instead of using the ChickHEN R2 TIff again, you can use ChickHEN R2 Signed EBOOT which runs directly from XMB. But you have to use the Tiff for the first time.
-> If you get a white screen after the Sony Logo, just press start+select+square+triangle simultaneously as you boot your PSP. This is format Flash1 and restore
The PSP battery must be above 75%
for safety reasons.
Enjoy. Hope this helps.