You will probably need to change or add a new account on your phone. its easy if you go into the Accounts & Sync tab from the settings area. You can create a new account and delete your old one. The google stuff should download automatically upon using the new account. I tried to find a place where you could just change the password, but I couldn't find it.
If you change your gmail password on your computer, then try to change it on your droid x, you will have the makings of a bad day, but don't fret, be patient. I can do it on my yahoo account on both devices. But the gmail will only let me sync the account. ...........Then a few minutes later you will get a notice saying your gmail will not sync and it gives you an authentication box. After you get that to work, you will be asked for the new password, and then another authentication box and your all done.
I looked up that problem on the forum because I had just changed my email password in gmail, and while reading the site, the solution I presented occurred. I thought it might be helpful for others that had the same issue too.