Cannot use ASG software license on ASG42x device.

Are you trying to install a Home Use License on this Sophos device?  To my knowledge that doesn't work without reloading the device with the ISO after taking some steps prior to loading it.  

I am new to this position and I found that a Home Licence was installed to this hardware appliance and the problem is that we are a school and I can not reinstall the appliance. I just needed to activate the remote access feature but the menu is greyed and I can do nothing unless renewing the license where I am stuck now.

You will most likely need to get a hold of a Sophos Reseller in your area to obtain the license.  Home licenses aren't supposed to be used in that fashion.  I'm sure there would be a big educational discount on a license.

Salut Mohammed et bienvenu - welcome to the UTM Community!

As Amodin says, your school will need to pay for a renewed license.  Your reseller can arrange for a demo license to get you through a few days while waiting for your license renewal.  Your license has expired, so only the firewall capabilities are available.  The free home-use license should not be used on that ASG in a production environment.

Cheers - Bob