Please could somebody suggest me the IDE which can use for AT89C2051 reprogram? I need make update in this old application and I don't want build whole once again. Thanks.

 

?? You need an IDE.. If you are not going build the program you just need a programmer!

I use several IDE's and a TL866.. My normal goto IDE, is a built in IDE to Proteus.. But any IDE can build 8051 code.
Eclipse... Textpad... AVR studio.. Keil ( free version ).. Is it a hex file or do you want to add code to the original source.

 

I’ve used both Keil and IAR.