Why is it taking more time, When i upgrade a module in Openerp
As you have said that You are new to OpenERP, Let me tell you something which would be very helpful to you. i.e Never Do changes in Standard modules not in base. If you      want to add or remove any functionality of any module, you can do this by creating a customzed module. in which inherit the object you want, and do the changes as per 
your requirement. 
Now regarding the time spent when upgrading base module, This is because when you update base module it will automatically update all the other modules which are already installed (in your case - Sales,Invoicing,Human-resource,Tools and Reporting) as base is the main module on which all the other modules are dependedent.
So, Better is to do your changes in customized module and upgrade that perticular module only, not the base.
Hope this will help you.
I'm new to Openerp.I have modified the base module and when i goto installed modules and search for BASE module and click upgrade button it is nearly taking 5mins.Can any one please say me how can i reduce the time that is taking for up-gradation of existing module.
Note: I have Messaging,Sales,Invoicing,Human-resource,Tools and Reporting modules installed,is it due to i have more modules installed??
Thanks in advance.