Twitter does not provide an automatic method to merge two or more accounts. This means that if you wish to consolidate accounts, you have to do so manually. It is better to undertake this task when you have few followers, so an early assessment of your Twitter account is a timely investment. Regular reassessments will prevent the transfer process from growing into an impossible task.
Three factors provide your identity on Twitter. The internal identifier for the account is your email address. You can only have one account per email address, so if you have more than one account, you must have two different email addresses – one registered against each account. The other two identifiers are your username and your name. The username, like your email address, has to be unique throughout the system. This is because Twitter creates a page for every member and this page is identified by the username. The name on your account is just an attribute that displays in a specific field on your page, and this doesn't have to be unique.
It's easy to tell which is your name and which is your username. The username is the one that appears after the "at" sign (“@”) on every comment you make. Your "name” in Twitter is likely to be your real name. If the account covers a company it will probably be the name of the company. The length of a username is restricted to 15 character and the name can't be longer than 20 characters.
The method Twitter recommends for “merging” two accounts involves changing the username and name on one of the two accounts. This does not really merge the accounts. It just enables you to make one account look like another account before you drop the mimicked account. Thus, if you want to merge “@bignose” and “@smallfeet” you change the username of @bignose to @bignose2, change the name of @smallfeet to @bignose and then drop @bignose2. If you have two different names on these accounts, update the details of @bignose to have that name.
The major flaw with this method is that your followers stick with the account, which secretly hangs on your email address, not the username or name. So renaming @bignose to @bignose2 and @smallfeet to @bignose just moves the followers of @smallfeet to @bignose and the followers of @bignose to @bignose2. You still have two separate accounts. When you drop @bignose2 you'll lose all of those followers. The recommended way to get around this problem is to manually set up the lists of followers of the soon-to-be-abandoned in the new account. This could be a strenuous task for people who have thousands of followers.