Can´t unistall Exchange 2010

I migrated from Exchange 2010 to 2016, I am trying to unistall Exchange, demote my "old" server to performe a clean install and then install Exchange 2016 and migrate it back to the "old" server.

Unable to understand what you are trying to do ?

Can you explain in simple language please

Are you trying to uninstall exchange 2010 and on same box are you trying to install ex 2016?

have you followed proper steps before uninstalling exchange 2010?

Firstly, move all your mailboxes to 2016 server
add new send connector to ex 2016
point your mx to 2016 server
change dns records - autodiscover and mail.domain.com records to point to ex 2016
move all arbitration mailboxes hosted on ex 2010 to ex 2016 -
New-MoveRequest DiscoverySearchMailbox* -TargetDatabase "EX16 Database"
Get-Mailbox -Database "name" -Arbitration | New-MoveRequest -TargerDatabase "name"

https://social.technet.microsoft.com/Forums/exchange/en-US/21e13b71-1ff9-4ada-9b69-914d3b6d7d3c/2010-to-2013-migration-and-discovery-search-system-and-federated-mailboxes?forum=exchangesvrdeploy

Then delete exchange database from ex 2010, point new ex 2016 database to new OAB generation server (ex 2016)
Then restart ex 2010 server once and then try to demote / uninstall it

as Mahesh mentions, have you removed all databases, oabs and public folder databases from old server? what versionb of EX2010 are you running? hopefully SP3 RU11

Sorry for my bad English...

I already did all steps mentioned above..  I have removed all databases, oabs, public folder databases from old server..  everything is pointing to the new server and in the new server.
The old server has SPE3 RU12.
I was thinking in removing the RU12 update but I am scared because before RU12 we had RU7, so I don´t know if it will break my Exchange 2016 in me new server.

I already turned off Exchange 2010 and everything Works fine....
The problem is when I try to uninstall Exchange 2010, it won´t let me.....  I am trying to find out the problem, my last resource is to manually remove Exchange 2010.

I give up....  I will try to Demote the server first, then, remove via adsiedit.msc the old exchange server, then I will format the server.... then I will install Windows 2012 and install Exchange again.

Do you think there will be a problem if I use the same server name after formating?

Using these steps wont be enough?
http://blog.dargel.at/2012/02/23/remove-legacy-exchange-server-using-adsi/

Thank for your comments, I couldn’t uninstall Exchange 2010, so, I had to Demote the old server, then format and reinstall Windows 2012, I used another different name so it will not cause problems in the future, I will remove all metadata using ADSI edit.

Thank you,