I thought this would be a good resource to share: http://lpsa.swarthmore.edu/Convolution/ConvolveGUI.html
1. Download source code from here: http://www.mathworks.com/matlabcentral/fileexchange/4883-convolvegui?controller=file_infos&download=true
2. Extract contents of folder to whatever folder you like.
3. In Matlab, right above the command window, there is a box that says current folder. You need use this box (or click browse for folder button) to point to the folder you extracted the source files to.
4. Type "ConvolveGUI" in the command window.
More information can be found via the link at the top of this post.
Hope this helps!