If you have encrypted any folders or have use EFS (encrypted file system) on your machine DE-CRYPT your information BEFORE you change ANYTHING about the accounts, If you change the name or the password on an account that uses EFS or encrypted folders you will LOSE ACCESS to those folders and files PERMANENTLY, you will NOT be able to access them again.

Reason:
When you use EFS or encrypt folders the encryption method uses your SID to make encryption/decryption key(s). Your SID is a number that is assigned to a user account that is really long and is guaranteed to be unique, even if you delete a user and create a user with the same user name and password that user will be assigned a different SID and therefore have different encryption/decrption key(s) and will not be able to access anyone elses encrypted information.