Marlin firmware update

I am trying to update the firmware for my Prusa i3 using the Marlin firmware provided by the supplier of my printer.

When I try to compile the sketch I get the following error (I have tried various board versions from 1.6.2 up to 1.6.14 but I get different errors depending on the version number)

Arduino: 1.6.13 (Windows 10), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"

In file included from sketch\SdFile.h:27:0,

                 from sketch\cardreader.h:8,

                 from sketch\Marlin_main.cpp:44:

SdBaseFile.h:38: error: using typedef-name 'fpos_t' after 'struct'

 struct fpos_t {

        ^

In file included from sketch\Marlin.h:10:0,

                 from sketch\Marlin_main.cpp:30:

c:\program files (x86)\arduino\hardware\tools\avr\avr\include\stdio.h:950:33: note: 'fpos_t' has a previous declaration here

 __extension__ typedef long long fpos_t;

                                 ^

exit status 1
using typedef-name 'fpos_t' after 'struct'

This report would have more information with
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You're using an outdated version of the Marlin firmware which isn't compatible with Arduino IDE 1.6.13. Please use the up to date version of the firmware. See: https://github.com/MarlinFirmware/Marlin/issues/5111