How to convert glucose to fructose
After searching on Google about Isomerization of Glucose to Fructose, you can find so many sources that explain the process. I think that this one is easy to understand among them. It explains that


  The isomerization of glucose to fructose is part of the glycolysis cycle that converts glucose to pyruvate. The way this is done is to isomerize the aldehyde (hemiacetal) glucose to the ketone (as a hemiacetal) fructose,and make another phosphate ester. The isomerization takes advantage of the ease of breakage of a C-H bond which involves a carbon next to a carbonyl carbon.


This gives a clear Idea on the mechanism of Glucose Isomerage to fructose. :)

Also see this.