Please do as following steps:
1. Start your virtual machine. Then open terminal application(Finder > Applications > Utilities > Terminal)
2. Copy the following command, past it into Terminal window and press Return:
prlctl list --all
The output should look like the following:
UUID STATUS IP_ADDR NAME
{3e21f02b-9d52-4ebe-a079-675dc822d723} running - Windows 7
3. Copy the following, past it into Terminal window and add space, and copy the UUID from the output of the previous command (e21f02b-9d52-4ebe-a079-675dc822d723 in the example) and past it at the end of the "prlctl set" command (do not forget that there should be a space between "set" and UUID number), then add space, type the following and add one more space:
--userpasswd
Right now you will have something like:
prlctl set 3e21f02b-9d52-4ebe-a079-675dc822d723 --userpasswd
4. Add username (your Windows user account name), colon, and a new password (do not add space between username, colon and password). Please see the example below:
prlctl set 3e21f02b-9d52-4ebe-a079-675dc822d723 --userpasswd yourWindowsUsername:yourNewPassword
5. Press Return. You should see the following:
authentication tokens updated successfully.
You can now login to your Windows user account using the specified password.