For an index the job are getting queued when ever the users runs the searchs.
Please let me where to increase/tweak the quota.
Did you first go to the Job Manager to remove the user's old jobs? That will free up some quota and allow the user to search again.
To change the quota, go to Settings->Roles and select the user's role. Then go to the Resources tab and scroll down to Disk Quota. This change will increase the quota for all users in the same role. If you wish to change only one user then create a new role for that user.