NO. Read what SixFlagsFiesta and ItalianPnoy112 said from the start. Ignore these other n00bs. You don't have to uninstall anything.
1. With just ONE TRACK, ANY NL TRACK right click on it, and choose Open With->Choose Program...
2. Find c:/program files/nolimits coasters v1.6/, and double click on NoLimitsEditor.exe or NoLimitsSimulator.exe (up to you).
3. Check Always use this program to open this kind of file. Click Okay.
Now ALL nolimits tracks will automatically open with the new version, as easy as one, two, three-point-one-four. (That was lame.)