switching from 32bit to 64 bit via system upgrade

I currently run 14.04LTS and note that the launch of 16.04LTS is imminent. I would like to install16.04 as 64 bit rather than my current 32bit OS.
1. Can I do this via the normal system upgrade when 16.04LTS is launched?
2. Will doing so retain my data files intact?
I Have looked at previous answers but they seem confusing. Some say yes others say it must be a clean install.
I believe that a normal version update to 16.04 LTS in 32 bit will keep existing data files safe.
But it is not clear if this applies during an version update and a switch from 32 to 64 bit OS.