Reconfigure FPGA

Hello,

I´m a newbie in the world of fpga and I introduced a doubt. I want to design hardware that has an FPGA (I also presents a similar case with a CPLD), and I wish that if there is any problem can upgrade the performance of the FPGA (new features, etc.), but it does not want to use the FPGA, and the user or the competition would have the file and could make copies. Rather, I mean it receives data and internally autoreconfigure or similar. This is doing with microprocessors, which have a bootloader and upgrade its flash (program), but I can not think of how to do it with an FPGA. Any help?. Thank you.

Greetings