If you have an r4 original, its v1.18. http://www.r4ds.cn/ If you have an r4 deluxe(clone), its v1.20. http://www.r4deluxe.com/ If you have an r4 SDHC(clone), its v.1.25. http://www.ndslr4.com/
There are 9 - yes 9 versions of the R4 R4 – Revolution (original) R4 SDHC R4 Pro R4 III R4 III SDHC R4 Advance R4 Deluxe R4 Ultra R4 New R4 revolution, will have no more software updates, the last is 1.18, however there is 1.19, this is unofficial it is the same as 1.18 but automatically adds the arm7 patch to solve the save problem. All the relevant software is available from http://www.linfoxdomain.com/nintendo/ds/
as dailun says " If you have an original, genuine R4 that is it and all there is ever likely to be " v1.18 . any other firmware version above v1.18 is for the vast amount of fakes , copies and clones that is being sold . it would seem a lot of manufacturers are taking advantage of the r4ds brand , but to be honest i wouldnt buy any of them . they are very cheaply made with head scratching versions of firmware . woof811.