Well, I don't know that you could flash different firmware (for whoever your carrier is now) on that phone, and even if you did, it would have THEIR bloatware on it. There's really only two things you can do:
1. Root the phone as it is, then use a tool like Titanium Backup:
http://market.android.com/details?id=com.keramidas.TitaniumBackup to remove the bloatware. Be sure to make a backup before you get rid of apps in case doing so has unintended consequences.
2. Load an AOSP/AOKP ROM, which won't have any/much bloatware. Learn to do without some of the features working the way they do with the stock ROM.
Frankly I wouldn't recommend either route - just read all of the stories from people that have trashed their phones; voided the warranty; etc, because they had no idea what they were doing. Is it really worth all of that to get rid of some carrier's crapware? Just hide the stuff in the app drawer and disable what you can.
But, as you said, it's your phone...
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM -0.001 using Tapatalk 4