i am a business and have the casio qt 8100 cash register.I am wanting to change the VAT to 20% on the plu's but do not know how to does this for all plu's as a whole rather than changing each individual one. Any help would be very appreciated

The 8100 was a pc based terminal and could be running any epos software, so without knowing what software you are running, no one on here will be able to help.

But, you probably just need to change the rate and not all the PLUs. There should be a tax rate / vat rate programming option on software somewhere.

Find out the actual software and someone here may be able to help.