The password length for Unified Authentication System, which manages passwords for some University-hosted computer systems, was 6 to 8 characters long.
Now the length have been extended to 8-16 chars.

You don’t have to change your password.
Even if you are using password of length 6 or 7 characters, you can use it without problems.
(Although you have to choose longer password when you change your password.)

But, since longer passwords mean enhanced security in general, we recommend you to use as long a password as possible.

You can change your password from:
https://account.tsukuba.ac.jp/cgi-bin/changepwd.cgi?lang=EN