Installing Custom Firmware 3.90 M33-3. This article assumes that you have custom firmware (OE/M33) installed on your PSP and want to upgrade to version 3.90 M33-3.

If you have OE/M33 firmware lower than 3.52 M33 please start from Section A.
If you have OE/M33 firmware greater than 3.52 M33 and lower than 3.52 M33-4, please start from Section B.
If you have OE/M33 firmware greater than 3.52 M33-4 and less than 3.90 M33, please start from Section C.
If you have OE/M33 firmware greater than 3.90 M33 and less than 3.90 M33-3, please start from Section D.

Downloads:
(DL.1) All versions of custom firmwares that are used in this article can be found at Dark_AleX’s site
(DL.2) Official firmware update 1.5
(DL.3) Official firmware update 3.52
(DL.4) Official firmware update 3.90

Section A - Install custom firmware 3.52 M33

Files to be downloaded and extracted:
(a) Custom firmware 3.52 M33 from Dark_AleX’s site (DL.1)
(b) Official firmware update 1.5 (DL.2)
(c) Official firmware update 3.52 (DL.3)

Steps to install:
(A.1) Copy the folder M33CREATOR and its contents to your PSP’s memory sticks’s /PSP/GAME150/ folder (eg. Z:/PSP/GAME150/).
(A.2) Rename Official firmware update 1.5 (EBOOT.PBP) to 150.PBP.
(A.3) Copy the file to your PSP’s memory stick’s /PSP/GAME150/M33CREATOR/ folder (eg. Z:/PSP/GAME150/M33CREATOR/).
(A.4) Rename Official firmware update 3.52 ((EBOOT.PBP) to 352.PBP.
(A.5) Copy the file to your PSP’s memory stick’s /PSP/GAME150/M33CREATOR/ folder (eg. Z:/PSP/GAME150/M33CREATOR/).
(A.6) In your PSP, browse to your Memory Stick and run the program 3.52 M33 CREATOR.
(A.7) After it completes, run the the program 3.52 M33UPDATE.
(A.8) Your PSP is now running custom firmware 3.52 M33. You can now delete the folder M33CREATOR folder from your PSP.

Section B - Update to custom firmware 3.52 M33-5

Files to be downloaded and extracted:
(a) Custom firmware 3.52 M33-4 from Dark_AleX’s site (DL.1)

Steps to upgrade:
(B.1) Copy the folder M33Update4 and its contents to your PSP’s memory sticks’s /PSP/GAME150/ folder (eg. Z:/PSP/GAME150/).
(B.2) In your PSP, browse to your Memory Stick and run the update (the icon has a grey background, with red letters saying 3:33:33 in the foreground).
(B.3) Your PSP is now running custom firmware 3.52 M33-4. You can now delete the folder M33Update4 folder from your PSP.

Section C - Install custom firmware 3.90 M33

Files to be downloaded and extracted:
(a) Custom firmware 3.90 M33 from Dark_AleX’s site (DL.1)
(b) Official firmware update 3.90 (DL.4)

Steps to install:
(C.1) Copy the folder UPDATE and its contents to your PSP’s memory sticks’s /PSP/GAME/ folder (eg. Z:/PSP/GAME/).
(C.2) Rename Official firmware update 3.90 (EBOOT.PBP) to 390.PBP.
(C.3) Copy the file to your PSP’s memory stick’s /PSP/GAME150/UPDATE folder (eg. Z:/PSP/GAME150/UPDATE/).
(C.4) Go to Recovery mode (Power off your PSP by holding the power button for 10 seconds. Turn on your PSP while holding the right shoulder button to go into recovery mode). Revert your kernel to 3.52.
(C.5) In your PSP, browse to your Memory Stick and run the program 3.90 M33.
(C.6) Your PSP is now running custom firmware 3.90 M33. You can now delete the folder UPDATE folder from your PSP.

Section D - Update to custom firmware 3.90 M33-3

Files to be downloaded and extracted:
(a) Custom firmware 3.90 M33-3 from Dark_AleX’s site (DL.1)

Steps to upgrade:
(D.1) Copy the folder UPDATE and its contents to your PSP’s memory sticks’s /PSP/GAME/ folder (eg. Z:/PSP/GAME/).
(D.2) In your PSP, browse to your Memory Stick and run the program 3.90 M33-3.
(D.3) Your PSP is now running custom firmware 3.90 M33-3. You can now delete the folder UPDATE folder from your PSP.