Start a new project. Set the tempo that you want the loop to be changed to as the tempo of the project.
Go into channel settings of the channel your wav file is in. There's a place on the first tab named "Time Stretching". Right click "time", hit auto. Type in the ORIGINAL BPM of the loop wav file, and presto. When you play the loop, it'll be played at your project tempo instead of its original tempo.
After that, right click the waveform picture and hit "save as" and put it wherever you want it.
It's actually way easier in FL10, so you should upgrade. (it's free unless you bought FL as a boxed copy). In FL10, it's easier. You can just drag the wav file to the clip playlist from the sound browser, hit the clip options and press "Fit To Tempo" after entering the original tempo. If it's a clear and concise recording, it should be able to automatically guess the correct BPM of the file. But it makes mistakes a lot, too.
Though FL Studio's time stretcher isn't perfect, I don't know if you feel like dropping $400 to use the one in Kontakt 5, so this is a pretty good option.