Visual Studio, Find and replace, regex

For versions before Visual studio 2012:
It works when I do this:
find include "{[a-zA-Z]+\.h}",
replace with include <\1>.
The most relevant parts for your question are the curly braces {} and the back reference \1: \n references to the n'th group indicated by curly braces in the search expression.

For versions Visual studio 2012 & up:
Starting with VS2012 .NET Framework regular expressions are used. So there it should be:
find include "([a-zA-Z]+\.h)",
replace with include <$1>.

You need to select both Match Case and Regular Expressions for regex expressions with case. Else [a-z] won't work.