You can uninstall or removes an installed alter-sequence-alignment package itself from Ubuntu 16.04 LTS (Xenial Xerus) through the terminal,
$ sudo apt-get remove alter-sequence-alignment
If you would like to remove alter-sequence-alignment and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove alter-sequence-alignment
If you use with purge options to alter-sequence-alignment package all the configuration and dependent packages will be removed.
$ sudo apt-get purge alter-sequence-alignment
If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.
$ sudo apt-get purge --auto-remove alter-sequence-alignment