Hi Ali
In general roles access permissions is changed through the Site Administration block on teh home page.
Select Users > Permissions > Define roles and select the role you want to change and edit.
This will bring up a choice of permissions grouped by capability - with the option to Allow prevent Prohibit and warnings.
It is probably best to select the role you want to change and choose duplicate role which means the orginial role settings are kept intact.
To see the effect of the change in role setting use the Switch role to box in a course (this isn't 100% accurate though so logging in as a person in the role should also be used)
Each role can be assigned at different context levels - eg system , course category, course see http://help.totaralms.com/Assigning_roles.htm for more detail.
As for your query on how to make profiles of all users available to the learner role - I can't see a setting for this . There is one called moodle/user:viewdetails which is already allowed for courses. According to the Moodle website there is one moodle/user:viewalldetails that looks as though this would do this but I can't see this.
Craig