On the XMB (the main screen) of the PSP, go all the way to the left most icon. Once there, go up to the top one in that column, it will say "Network Update." If you have a wifi connection set up on your PSP, hit X to go into the update checker. Once it connects to the server, it will check for updated firmware. If you have the newest version, it will tell you so, but if not, it will prompt you to download the newest one. It takes about 25-26MB on a memory stick. once the thing downloads, you can start installing the update, but you can't install it if your PSP is plugged in to the AC adaptor. Once the installation starts, it takes a few hits on the X button to confirm things, then it does its thing. Once your PSP restarts, you can delete the firmware update from your Memory stick. To do that, go to the game icon on your XMB and go down to the one that says Memory stick. the firmware will show up, hit triangle to bring up the options, and then hit delete.

That's a hard question to answer...