Hey there. The Ally was my first Android phone. Let me see if I can help.
You are rooted, yes?
Good. You need to flash recovery. The easiest way is to download ROM Manager, open it, give it root permission, scroll to the bottom, as flash AmonRa Recovery. Next, download Velocity 1.2.2. It can be found in the All Things Root section of this forum.
Now, boot into recovery. This can be done using as app called QuickBoot.
Once in recovery, using volume buttons to scroll and the power button to select, choose Backup/Restore. Now choose Backup. This will create an snapshot of your phone before we wipe it and flash Velocity. That way, if you don't like Velocity or whatever the case may be, you can always go back where you were.
Once the backup is made, Wipe data, wipe cache and in the advanced menu wipe dalvik cache. Once that is handled, choose flash zip from SD card. Navigate to the zip and select it to flash.
When that is all done, reboot and sign in to your gmail account to regain all your contacts and emails, etc. You will notice that Velocity has less bloatware apps and some useful apps to enhance your experience.
Hope this helps.
jmar
Velocity: use open beta 18. It is the last version this ROM:
http://androidforums.com/ally-all-things-root/479960-velocity-1-2-2-open-beta.html#post3777099
This is a helpful place if I forgot to mention something.
http://androidforums.com/ally-all-things-root/162822-lg-ally-rom-root-guide-faq.html#post1483320