This is my guide on how I upgraded to Android 2.1 on my Motorola Milestone (UK).
What you need:Please, no noobs. You must have some knowledge of using ADB and you must have the Android SDK installed. I am not responsible for ANY issues you run into. Try this at your OWN risk.
1) Rooted Milestone
3) A 2.1 Nandroid Backup - Check the 2nd Post for Them
4) ADB Driver (64Bit Here)
Install the ADB Drivers
If you do not already have the ADB driver, download the ADB drivers above and install them.
Download the Nandroid Backup (Thanks The Solutor and DAGr8)
Download the Nandroid Backup above (either the stock or modded). On your sd card create a folder called 'Nandroid'. In the Nandroid folder create a folder called 'console=ttyS2,115200n8' then extract the Zip file you just downloaded into this folder (which should be a folder containing files).
Download the ADBRecovery (Thanks poseidon)
-In the Zip file there will be a Recovery folder and a update.zip file. Drag both of them to the ROOT of your SD Card.
-You should have an update.zip and a folder called 'recovery' on your sd card.
Now make sure you have set up the Nandroid folders correctly and you have the 'Recovery' Folder and the 'update.zip' file on the root of your sd card. If so, your good to go.
-Connect your device to your PC and Power off your phone
-Hold the CAMERA button and then press the POWER button and HOLD them both until you see the recovery screen.
-Once you see the recovery screen press the VOLUME UP button and the CAMERA button at the SAME TIME until you see a menu.
-Select 'wipe data/factory reset' and then select 'yes'
-Select 'wipe cache partition'
-Select 'apply sdcard:update.zip'
-You are now in ADBrecovery. On your PC open up a Command Prompt.
-'cd' to your Android SDK tools folder (mine is C:\android\tools)
-then type 'adb shell'
-then type 'su'
-then type 'nandroid-mobile.sh restore'
-then just hit your Enter key on your keyboard
-then hit your Enter key on your keyboard again
-let it restore the Nandroid backup
-Once it says 'Restore Done', on your Milestone select 'reboot system now'
You are now rebooting into either a stock 2.1 ROM with root or a 2.1 ROM which is already rooted and has some mods to increase speeds.
For many more 2.1 Nandroid Backups visit this thread and download whatever one you want and follow my instructions. I chose the two best backups to use.