Use InStr(), it returns the location of the first character matched.

Code:
x = InStr(htmlHere, "<span class-""given-name"">")
if x > 0 then do_something 'it found a match
'to find the next result, the end of the field:
x = InStr(x+1, htmlHere, "</span>") 'here I use X+1 as a starting point, it won't search before this location, only after

'do this over again for the family-name