Don't delete anything -
Register & map the new name 10kpoems.com to the proper base blog - that can be the same blog as ridwanmao.com is mapped to.
Select 10kpoems.com as the Primary Domain when you do the mapping - the will change the Primary Domain away from ridwanmao.com if you map to the same base blog - 10kpoems.wordpress.com
Then go to the Store and make sure you have the domain registration and mapping for ridwanmao.com set so they will not auto renew. You should be able to let ridwanmao.com just go off into oblivion - should not hurt anything -
There is another option since your site does not look like it has any content in it - have you sent out the domain name ridwanmao.com to anyone? Do you care if the domain goes into oblivion now? If not then after you buy 10kpoems.com we can ask the staff to transfer the domain mapping to 10kpoems.com and save you $ 13.-- if they transfer it (I am sure they would)