How to remove server instance as a windows service?

Create a script called removeSvc.cmd and copy the following lines. Make sure adminServer name & domain name values are correctly set. And execute from the same place(c:\bea\wlserver_10.3\server\bin) where you created window service before.

echo off
SETLOCAL
set DOMAIN_NAME=sampleDomain
set SERVER_NAME=AdminServer
call "c:\bea\wlserver_10.3\server\bin\uninstallSvc.cmd"
ENDLOCAL

The name should be matching with the name given at the time of creating service in installSvc.cmd.