This post will guide you through the necessary steps to achieve a successful Ubuntu installation, alongside Windows 8.
Be aware that dealing with partitions is a risky job if you don't know what you're doing. You can do permanent damages and lose data.
Step 1: Windows Backup
In the Windows Start menu type: “Windows 7 File Recovery” and select that option.
For some weird reason, although this is a Windows 8 machine, this tool is still called “Windows 7 File Recovery”.
On the left panel, select “System Repair Disk”.
And then also a “System Image”.
Make sure you complete those actions
Step 2: Reducing Your Windows Partition
Right click over “Computer” and select “Manage”, then “Storage” and then “Disk Management (local)”.
Right click the Windows partition, and select “Shrink Volume”.
Then you can select how much space you want shrink from the Windows partition. In our case, we selected around 250GB because the disk was 1TB and we’re only using about 55GB (yes, the images have different values because they were taken afterwards, just ignore that :P ).