I propose to use the Gparted live ISO that can be downloaded here
https://sourceforge.net/projects/gparted/Before starting backup your disk, just in case something goes wrong.
I will explain what I would do to achieve this.
1- Default size of 50GB

2- Go to File -> Virtual Media Manager (Ctrl+D) and select the correct disk

3- Increase the disk size as you want (I used 75GB as example)

4- Go to the setting for your VM, Storage, and add a new empty optical drive

5- Select your gparted-live ISO image and boot

6- Once booted, open the Gparted application and you will see something like this.

7- Add the unallocated space into your disk

8- In the end, if everything went as expected you will have a larger disk in your environment

I hope this information helps you. Regards!