Windows OS residing in `/dev/sda5` in the figure you've shown. In your system it's the only `ntfs` partition large enough to hold windows installation.

You can easily mount and see which partition containing what and decide to remove them. Like in Windows installation partition you'll find folders relevant to windows. To mount `ntfs` file system in Linux you need `ntfs-3g` driver, which usually comes inbuilt with Ubuntu. Otherwise install it using `apt install ntfs-3g`.

In your system `/dev/sda1` is mounted as `/boot/efi`. So, it's containing `grub` boot loader. So, don't delete it even by mistake. You can delete `/dev/sda2-/dev/sda5` and `sda6, sda7`.

If your main purpose is freeing up disk space I'll suggest you to delete `/dev/sda5` only. Other partitions mentioned above has windows recovery, Windows bootloader etc. They may be helpful in case of a factory restore etc.

Now merging the entire 1 Tb disk is a tricky job. For that you've to first delete all drives except `sda1, sda8 and sda9`. Then merge all the space and copy all contents of `sda8` i.e. Linux root partition into the newly created partition using **`rsync`**. Then you've to change `/etc/fstab` entry properly and boot the system with new file system as root. Also change the `root` parameter in `grub` to the new partition. 

Once the system is booted with new file-system as `/` you can delete the existing root file-system i.e. `/dev/sda8` and merge it with the new created root file system. 

**NOTE** Changing root drive is a hazardous job. If not performed correctly your current installation may stop working. Another easy solution is delete all partitions and reinstall Ubuntu freshly. Always have a backup of all necessary files before deleting anything.