How to clear NPOI WorkBook memory.

Feb 15 at 11:59 AM
I am using NPOI dll to read excel file which contains 35k rows(10MB )
using (FileStream fs = new FileStream("temp.xlsx", FileMode.Open, FileAccess.Read))
      IWorkbook wb = WorkbookFactory.Create(fs);
After reading excel file using above code process memory increased around 200MB. In my application multiple excel files are reading one after another, so process memory increasing for each file. I am unable to clear process memory because workbook doesn't have any dispose method. I want to clear memory occupied by workbook after completion of work with one excel file and read another file.
After reading excel file : Is there any method to clear workbook memory?