an error occured during signature verification Ubuntu 19.04

[Tapas Mishra]

Hi,
I am using a virtual machine downloaded from here
https://www.osboxes.org/ubuntu/#ubuntu-19-04-vmware
when I do
osboxes at osboxes:~$ sudo apt-get update
[sudo] password for osboxes:
Get:1 http://security.ubuntu.com/ubuntu disco-security InRelease [97.5 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu disco InRelease [257 kB]
Err:1 http://security.ubuntu.com/ubuntu disco-security InRelease
  The following signatures were invalid: BADSIG 3B4FE6ACC0B21F32
Ubuntu Archive Automatic Signing Key (2012) <ftpmaster at ubuntu.com>
Get:3 http://us.archive.ubuntu.com/ubuntu disco-updates InRelease [97.5 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu disco-backports InRelease [88.8 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu disco-backports/universe
amd64 DEP-11 Metadata [7,924 B]
Reading package lists... Done
W: An error occurred during the signature verification. The repository
is not updated and the previous index files will be used. GPG error:
http://security.ubuntu.com/ubuntu disco-security InRelease: The
following signatures were invalid: BADSIG 3B4FE6ACC0B21F32 Ubuntu
Archive Automatic Signing Key (2012) <ftpmaster at ubuntu.com>
E: Repository 'http://us.archive.ubuntu.com/ubuntu disco-updates
InRelease' changed its 'Suite' value from 'disco' to 'disco-updates'
N: This must be accepted explicitly before updates for this repository
can be applied. See apt-secure(8) manpage for details.
osboxes at osboxes:~$

What should I check here?
How can I resolve this problem?
----------------
Thanks
Tapas