If I switch antivirus systems do I have to remove old system before I install the new software?

You can but you don't have to if you still wish to keep the

old anti virus.

At least you have some for of comparison for your new anti

virus system. Sometimes firewall may slightly conflict but it is ok with extra firewall.

As for me I have Norton and AVS Anti Virus

and Norton and ZoneAlarm Firewall running at the same time.

No issue.

If I switch antivirus systems do I have to remove old system before I install the new software?avast

I would, since the 2 programs might interfere with one another.

If I switch antivirus systems do I have to remove old system before I install the new software?ducati

yes, sometimes the programs won't work well if there are 2 antivirus programs going.
Yes, you should uninstall the old one, then install your new one..Never run two anti-virus programs, at the same time. Do not have two firewalls, on your system, at the same time..Just use the one, that you are most comfortable with..
From experience, McAfee and Norton Antivirus just don't work hand in hand. More often than not, its better to remove your previous antivirus, since it would make your pc more stable.