In my ubuntu 10.04 pc the files that are stored in /home/myusername folder gets copied to Desktop automatically. When I delete the files in Desktop the files from home directory is also deleted. But I can't copy these files to home because it says file exists and whenever I press Merge button it shows some error
As iBelieve says, you want the opposite of the solution to this question. (And it's strange that your desktop shows the contents of another folder without you having deliberately configured it to do so, but I've heard of that before.)
Specifically, what you should do is to open the file
~ stands for your home directory. One way to open the file is to open a Terminal window with Ctrl+Alt+T and run
gedit ~/.config/user-dirs.dirs. Or you can run that command in the dash textbox or Run... dialog box raised by pressing Alt+F2.)
With the file open in the text editor, find the line that says:
Make it say
instead. Save the file, and quit the text editor. To apply this configuration change, log out and back in (or, if you prefer, reboot).
Finally, please note that the desktop version of Ubuntu 10.04 LTS is no longer supported. It doesn't even get security updates for newly discovered vulnerabilities, so it is dangerous to use! You should upgrade to a supported version of some operating system--perhaps to Ubuntu 12.04 LTS.
Ordinarily we would close a question about an unsupported release (and it's possible that will happen here). However, this is one relatively rare case where your quetion is similar enough to an existing question that we can know the solution applies generally, while still different enough probably not to be a duplicate.
If you choose to upgrade and need any help, please feel free to post a (separate) question about that.