Changing Raid from 1 to 0

You will lose your data. RAID 0 uses a stripe across both disks. That is, one block gets written to disk A, the next to disk B, the next to A, the next to B, .... That is, each disk only holds half of the data stored on the set, but it's every other block of data, not contiguous. Once you split the RAID 1 mirror, and then try to rebuild it into RAID 0, you have nothing. Maybe you should look at JBOD instead which will probably let you keep your data and grow across both disks. If you want the performance of the RAID 0 stripe, you'll need to reinstall everything.

It goes without saying, but make sure you have all the backups you need before getting started.

As said above, just removing a partition will end badly.

You can copy all the data off the raid1. Then destroy the raid1. Then create the raid0. Then copy data back to raid0. This will work for data, not boot partitions.

If you're talking changing your boot drives to raid0, that will require cloning/mirroring. Clone the raid1 to an image or temp disk, destroy the raid1, create raid0, restore the clone to the raid0. This would require physical access to the computer and a temp disk with space for the cloned image.

First to have raid 0 is very bad idea. Doesnt matter if you put 2 or more disk in raid 0 if just one of them fails ALL your data is permanently lost. Then you made a post with "I just don't want to lose the data". So which one holds the ground, can you lose your data or not?

If the answer is you cant lose your data then why you want to change from raid 1 to raid 0? Either way whatever you do i would suggest to make a full backup of your server because just one little mistake and all your data will be lost forever.