Wireless Access

There's an area in our warehouse where wireless signal is very bad, wireless router is right above in that area, signal keeps dropping on and off in scanners in that area only , please advise on repair needed

What kind of access points do you have and how high are they mounted?  Typically there is  "null" right below access points, so you have to have overlapping AP coverage to provide coverage right under an AP.

I will be honest with you:

You need to send someone onsite to the warehouse to survey the coverage and see what is going on.  A warehouse is one of the most difficult deployments because there are so many objects that can affect wireless.  There is little chance we can figure out what is going on on this forum when nobody is onsite to check things.

are there changes in the antenna that I can make for connecting in an area like a warehouse. This is an aruba model 103 and its 45 feet high. other aps in the area are working. Devices make connectivity and then they drop 

A warehouse is the most complicated deployment, period.  There are many reasons why this would happen, including physical barriers.  Is there clear line of sight betwee your clients and the AP?  Someone needs to visit the Warehouse and Survey the area to see what is the signal strength received from the AP around it.

I can look via airwave and notice that the signals starts looking good and seconds later signals drops and clients drops. 

There is a delay between when client signals are measured and when they are reported.  Even APs might only report client signal strengths once per minute.  It is not in realtime.  You would have to measure that onsite to determine what is really happening.

I replace a bad AP but i want to change it to default.

The New AP I want replace it with original name (seeing MAC Address)

If the old AP is down, you need to clear that ap's name from the controller first by clicking on the "Down" AP number and clicking on clear.  You can then reprovision the new AP by going to configuration> wireless> AP installation.  You can then select the AP, click on provision and change the mac address to the old name.