First, uploading a picture is different for Users and Instructors. There exist many different LMS configurations, versions also. First you need to check in your system if the picture field is available or not.
Navigate to System Admin -> Configuration -> Record Configuration -> Select a record to configure (User) -> Select the tab Basic Configuration -> Have a look if in the sub-tab "Display". There you can find the field Picture and if its checked. It should be checked.
Navigate to Users -> Search for your User ID -> Open your User -> Click/Expand the "View All" section -> move to the field Picture -> Click Edit, select a picture and upload it.