Your best bet is to remove all your previous AV software manually through your Windows Control Panel.
If you run into problems installing Trend Micro™ Titanium™ Security before getting rid of your old antivirus software, check out this Trend Micro Knowledgebase article for help: http://esupport.trendmicro.com/solution/en-us/1058894.aspx
Got a security question? Ask Vic
I work for Trend Micro and all opinions expressed here are my own.