Hi Zehran,
Please perform transaction KEA0, menu -> Extras->Characteristics->Unlock. Then, you can make the used characteristics changeable and move the one you wish to delete to the right side. When you activate again the tables will be converted. This can take some time, depending on the size of the tables. If you want to remove the characteristic completely, you have to remove affected char. as segment level characteristic in KEQ3, then run where-used list in KECM for char. and finally run KEQ3 from the where-used list result. Here you are able to remove the characteristic from the list completely.
Regards, Gordon