I want to change the group settings (oGrp.OnlyAllowMembersViewMembership = false) for all the site groups present in my site. I have to use web services to perform this function and not the object model.
Until now I have worked on the object model mostly so I'm not very sure of web services. Please let me know if anyone has ideas on how to go about it.
I don't believe this is possible using the web services. They have a more limited set of functionality than the object model. It is possible to add and remove users from groups but there is little that allows you to change a group's settings. UpdateGroupInfo is the closest I know of which doesn't do what you want.
Your best option is to write your own custom web service and deploy that. You can then use the SPGroup.OnlyAllowMembersViewMembership property from the object model to configure the groups.