This page is aimed those upgrading their GEMPACK and wondering whether to also move to the Intel Fortran compiler.
LF90 is rather old and partially incompatible with modern versions of Windows. It is not supported by current releases of GEMPACK. We recommend that you move to the Intel Fortran or GFortran compiler.
There is no immediate need to change compiler if you do not have any performance issues with LF95 executables. Such issues may be long run times and accessing enough memory. Intel Fortran produces executables that on average run a bit faster than LF95, see here. If run time is very important to you then you could move to the Intel Fortran 32-bit compiler and see a speed improvement. This is a relatively simple upgrade on a current Windows computer. Upgrade tasks would be: obtain and install Intel Fortran, obtain and install GEMPACK.
The most memory an LF95-created executable program can access is 2 GB. If you find your models are constrained by this limit (ie. you have at least 3 GB RAM in your PC and your model cannot access enough memory) then you should consider moving to the Intel Fortran 64-bit compiler. This is a bigger upgrade since for most people it will involve carefully considering their PC hardware and operating system. Upgrade tasks would be: Obtain PC with 64-bit Windows with at least 4 GB RAM (but more sensible to get 8 GB RAM if budget allows). Obtain and install Intel Fortran 64-bit. Obtain and install GEMPACK.
If you buy Intel Fortran you get both 32-bit and 64-bit versions. You could try 32-bit and move to 64-bit later (this would mean re-installing GEMPACK).
You can read about obtaining/prices for Intel Fortran here.