update install_windows.md

docs/install_windows.md

-# How to install on Windows
 
 
+#Install wetb on Windows
+
+For updating the toolbox jump to [Update wetb on Windows](#Update wetb on Windows)
+
 This guide describes how I installed the toolbox on a Windows machine (1/9-2016)
  
 - Download and install Anaconda (Python 3.5 version, 64bit installer) from <https://www.continuum.io/downloads>
@@ -57,4 +60,17 @@ pip install pyscaffold pytest-cov --no-deps
 ```
 pip install wetb
 ```
-     
+
\ No newline at end of file
+[#Update wetb on Windows](#Update wetb on Windows)
+
+* Activate the envirronment (type in a terminal):
+
+```
+activate py35
+´´´
+
+* Update the toolbox
+
+```
+pip install wetb --upgrade --no-deps
+´´´