Looks like you missed the 6.4.1 altertable - you'll probably want to re-run it.
You can change a user's password by using the following command in the Database Tools -> SQL Command area:
update w3t_Users
set U_Password = md5("password")
where U_Number = 0
Replace "password" with the new password. Keep the quotes.
Replace 0 with the user's number. If you don't know the user's number, you can try:
update w3t_Users
set U_Password = md5("password")
where U_Username = "Display Name"
... replacing "Display Name" with the user's display name. Keep the quotes.
Do note that the email retrieval feature actually sets a temporary password instead of reminding the user of his current password. MD5 is a one-way function that can not be decrypted.