Good Morning t04st3r,
You can't merge your Apple ID accounts together. However, you can gather all of the purchases from various accounts and organize them into the one account that you wish to use moving forward. Click on the link below to see more details and screenshots. I've highlighted some key information for you.
Set up your Apple ID for iCloud and iTunes - Apple Support
http://support.apple.com/en-us/HT204053
An Apple ID is the email address you use as a login for just about everything you do with Apple, including using iCloud to store your content, buying songs from the iTunes Store, and downloading apps from the App Store.
When you set up your iPhone, iPad, or iPod touch, you can use the same Apple ID for both iCloud services and purchases on the iTunes Store, App Store, and iBooks Store. Or, you can also use one Apple ID for iCloud services and a different Apple ID for Store purchases (including iTunes in the Cloud and iTunes Match). You'll get all the benefits of iCloud whether you use the same Apple ID for iCloud and Store purchases, or different IDs for each. To change the Apple ID signed in to iCloud or iTunes on your iPhone, iPad or iPod touch, sign out and use the steps below to sign back in with the updated Apple ID.
Can I merge multiple Apple IDs into one?
No. You can't merge two or more Apple IDs into a single one.
Can I change the name of my Apple ID?

Yes. For example, if you get a new email address, you can change your Apple ID from your old address to your new address. @mac.com and @me.com Apple IDs cannot be renamed.
First, copy all of your purchased content so that it's on the same Mac or PC with iTunes. This computer should be the one you sync your device with.
Next, authorize your computer to play content with each Apple ID in iTunes. After your computer is authorized for all of your content, it can be synced to your iPhone, iPad, or iPod touch.
I hope this information helps ....
- Judy