Install Gmail 4.2 on 4.0+ devices [Root required]
November 3, 2012
Before we proceed let me mention two things, firstly your device needs to be rooted for this procedure. And make sure you backup your file or ROM before trying this.
Just download the apk from here and copy it to your sd card.
Method 1: Using Titanium Backup.
1. Open titanium Backup and locate the older gmail app.
2. Uninstall it.
3. Install the new apk using any file manager.
4. Go to your homescreen and press the menu button and select Manage Apps > and locate Gmail and clear the Cache.
5. Open Gmail and the newer version should work.
Method 2: Using a Root File manager.
1. Navigate to /system/app and locate Gmail.apk or find it in /data/app
2. Rename it to Gmailbackup.apk
3. Copy the new Gmail.apk to the same folder and reboot your device.