Resizing Windows VM screen size in Ubuntu 20.04

Open Devices from the File menu

Click Install Guest Additions CD image

Go to main directory of the computer with all the disks displayed

Click the CD Drive VirtualBox Guest Addtions

Double-click the VBoxWindowsAdditions.exe file depending on your operating system (x86 for 32 bit os and amd64 for 64 bit os) 

Press Right Ctrl + C to - This creates the VM windows with a proper resolution

Ubuntu 18.04 to 20.04 Error: Please install all available updates for your release before upgrading

  $ sudo do-release-upgrade

Checking for a new Ubuntu release

Please install all available updates for your release before upgrading.

$ sudo apt-get upgrade

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Calculating upgrade... Done

The following packages have been kept back:

  linux-generic linux-headers-generic linux-image-generic

0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.

$ sudo apt-get dist-upgrade

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Calculating upgrade... Done

The following packages have been kept back:

  linux-generic linux-headers-generic linux-image-generic

0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.

$ apt list --upgradable

Listing... Done

linux-generic/bionic-updates,bionic-security 4.15.0.135.122 amd64 [upgradable from: 4.15.0.34.36]

linux-headers-generic/bionic-updates,bionic-security 4.15.0.135.122 amd64 [upgradable from: 4.15.0.34.36]

linux-image-generic/bionic-updates,bionic-security 4.15.0.135.122 amd64 [upgradable from: 4.15.0.34.36]

$ dpkg --get-selections | grep hold

linux-headers-generic hold

linux-image-generic hold

$ sudo apt-get install linux-headers-generic

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following additional packages will be installed:

  linux-headers-4.15.0-135 linux-headers-4.15.0-135-generic

The following packages will be REMOVED:

  linux-generic

....

$ sudo apt-get install linux-image-generic

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following additional packages will be installed:

  linux-image-4.15.0-135-generic linux-modules-4.15.0-

$ sudo reboot

 $ sudo do-release-upgrade  --> This updated my Ubuntu 18.04 to 20.04