You can log in to Jira with a different user
1) Switch to User (USER and ADMIN)
Switching to another user is available from the user menu or by url in you Jira '/secure/jibrokSuSetUser.jspa' or Go to from admin search (hot key gg) 'SU Login as another user'
On the page that opens, you will have access to select users under which you can enter. Jira administrators are responsible for the accessible list.
Click Run as selected user
Everything! You are logged in under the selected user. At the end of the work, you need to exit Jira through the user menu.
2) How create SU permission settings? How delegated switch to user? (ADMIN)
Open url in you Jira '/secure/jibrokSuPermissionAll!default.jspa' or Go to from admin search (hot key gg) 'SU permission settings'
Admins('admin users' and 'admin groups') - users with the right to log in under other users.
Users('users' and 'groups') - users under which admins can log in.
3) All actions with SU Permissions and logins are recorded in the standard Jira audit log.