Addon domains are hard to do without downtime as a reseller, on the same server.

But essentially what you need to do is create the accounts in WHM, upload the files, and then when you are done, delete the addon domains. You might make sure a tech is handy to be there for you when you start deleting the addon domains because I have seen issues with cPanel getting confused and the site goes down, in which case you need someone with root access to the server to correct this.

The other option is to get another temporary hosting account, upload the sites to the remote server, point the domain's DNS to that one, which will safely avoid downtime, remove the addon domains in your main account, THEN make individual accounts for each domain in your WHM, upload the sites via FTP or transfer cPanel backups of them, then re point the DNS back to tour main server.

The last is the best way if you cannot afford downtime. If you want to risk a short while of POSSIBLE downtime then you can try the first method.

As for your quota issue, you could upgrade to accommodate more space, or, set your own package for ricknlisa.com. Currently it still sits on a 4 star plan but if you make your own packages in WHM you can free up some quota. ricknlisa is allotted 500 megs but only uses just over 300 of actual space. Make a plan that has 350 megs of available space for that site, then make packages for each site that match actual usage.

After you free up one addon domain you can edit one of those packages to allow more space. For example, ricknlisa.com should not use as much space after you ditch the addon domain in that account.