[Tip] How to self-update Cydia using the auto install feature
Since I only found it for regular apps, but not for cydia itself, I'll explain here how to do it.
Cydia allows you to install a certain app by only putting it on the AutoInstall, and reboot the phone.
The purpose is to update old verions of cydia, like 1.0.3366. This version is commonly installed with many jailbreak methods. The problem is that this particular version lacks the ability to update itself, so we'll do it manually. This should work with iPhone and iPad. Tested only on iPhone 3G with iOS 4.2.1, using redsn0w 0.9.6b5. Successfully updated from Cydia 1.0.3366 to 1.1.9:
1 - Your device must have jailbreak already and cydia too.
2 - Power on the device and connect it to the computer
3 - Download iTools 1115E software or equivalent.
4 - Download the deb version of cydia you want, for example from the Saurik apt. You can install other software too this way.
5 - Open iTools, wait until device is shown, click on Filesystem (jailbreaked), go to "/var/root/Media/Cydia/AutoInstall", click on Import file, and select the newer version of cydia in deb format. Wait until it's uploaded, should be fast.
6 - Reboot your device
7 - Open cydia again, and wait until asks for software updates.