Trying a new antivirus product

I could not get my Windows Defender to run a full scan so I knew that something was wrong. I replaced it with a free trial of Sophos which found something called NewNext which is malware disguised as adware apparently. The problem with Sophos is that it is set to update hourly and I cannot change the frequency.  So it makes my computer which is old but with a new HDD crash all of the time. Precious hours are going down the drain and the location of the computer - Caribbean versus Canada, makes no difference.