Now I have another question.
I read the text and now I can erase and program a certain adress,but I haven`t exactly understand if I can realise what I want to program.

My program starts at 0000h and ended at 7FFFh and my bootloader starts at F000h.

Now I want to realize a program, which jumps to the bootloader when I push a certain button on the keyboard.
And when I am in the Programming routine, I want to erase my old program and write the new modified program again in the flash from the adress 0000h.
Is this possible?
Because when I am in the Programming routine the BSEL bit is cleared and the Bootcode is activated but when I want to write my new programm to the adress 0000h I have to change to the User code and the BSEL bit had to be set.
My question:
Is it possible to be in the Bootcode and write the new program at the same time in the same adress block?