You will find it is necessary to uninstall ealrier version,also AVG Anti spyware and Rootkit programmes,apparently thes are now part of V8.They also suggest you shouldn't be running other antivirus programmes.
phew ! thanks guys my PC wouldn't let go of the old 7.5 some how ? as you rightly said Ian the AV and Anti Spy are all in one and I had better results when taken from there server rather than download to desk then install thanks again Tez