I am using ITUNES WINDOWS to backup my iphone, but my SSD doesn't have enough storage.
Is it possible to change the backup location to HDD before I start the backup?
By the way, my last backup is stored in C:\Users\Tan\Apple\MobileSync.
No, you can't.
but you can copy the backup folder off to an external drive after you have made the backup to free up room.
See this:
Locate backups of your iPhone, iPad, and iPod touch - Apple Support
When I need to restore backup, I will have to manually select the folder？
You may have to move the entire folder back, I am not sure.
Change Backup Location
