How to deinstall Ubuntu?

You may manage by simply reinstalling the second Ubuntu onto the SSD, then removing the first Ubuntu partitions using something like gparted from a live system. Do not remove the partitions first as you may then find that you can not boot either OS.

I think you must be very careful about the way you do this as it will depend upon what happened to your Windows boot files, whether the machine is using UEFI or MBR/BIOS, and what partitions you have where on the two disks. The safest way to proceed now is probably to run the Boot-info script from Boot-Repair in my signature, which will give you a pastebin link to show us which will have all the info needed to suggest your best course of action.