Can WHM copy account from other host ?
Can WHM copy the addon domain of an account of a cpanel host and make it main account ?

Yes, if the other Host is also using WHM.

No, the Addon Domain would have to be deleted then recreated as a regular account.

[No, the Addon Domain would have to be deleted then recreated as a regular account]
Can i delete the main domain and upgrade the addon domain to primary ?
Is there any other solution?

No other solution.

Understand what 'addon' means. If you delete the main account you delete everything connected to it -- including Addon domains.

Thanks for the info

Your welcome. :)