Of course, you can install pure Win10 (without Teclast customization), but I would not recommend doing that, because finding and installing the proper drivers may be a pain. Also, you may loose Windows activation (not sure about that). It would be much simpler to install Teclast version, then uninstall all Chinese garbage and update drivers (if something doesn’t work as desired).
Concerning the partitions, you may delete all Android partitions (ext4 and raw) and keep both UEFI partitions, Windows system and restore partitions. In my Teclast X86 Plus II tablet, partitions to keep are first two and last three (as they are located on eMMC), although it may differ. I strongly recommend first to make a backup of being deleted Android partitions in case you want to restore them later. I prefer doing that by attaching the USB hub with keyboard and bootable WinPE flash drive containing backup software. After deleting unnecessary partitions, you may want to combine free space and give it to Windows partition.
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