Google services provide several social media destinations, like Picasa, Google Reader, Orkut, YouTube and services like Blogger, Gmail and Google Docs. Many people find themselves stuck with an old primary email address associated with Google or perhaps several accounts assocaited with several email addresses wanting to funnel these services into one single account. Google does not make this easy.
You can not simply conflate your accounts. You can, however, change the associated email addresses and delete duplicate accounts.

At Google.com, log into your account and click on My Account. Next, click on Edit under the email address(es).

You may add additional email accounts for notifications. Type in the desired email address and click save.

When you click save, you will be required to verify the email address.

Check your email and follow the link provided in the verification email. You will be required to log in again.

Once verified, the address is associated with your Google account. You may have several email addresses associated with the account.
If you want to remove the primary email address from the account, this is not possible using this method. Once the primary account is set you can not change it for that account. You must delete the account and all its assocated products to remove the primary email address. Consider this when choosing an email address to use as a primary for your Google services.
If you delete your Google account to remove the primary email address, there is no way to salvage related data afterwards. It may be best to simply keep the old email address associated with your account and use the new preferred account as an additional email address.
To delete the account, go to the Google accounts page by clicking on My Account from the Google website. Click on edit next to My products.

After clicking on edit you will see an option to Delete a product, or the entire account.

Once you select Delete account, you will be once more asked if you wish to delete all associated services.

