Welcome to the forum!
In the project tree down the left hand side, down toward the bottom, you'll find the hardware configuration. Right click on your 1769-IF4 and select properties. Here, you can configure your card and define the scaling values for each channel. You *could* just scale it right then and there - so set your low scale to 0 and your high scale to 100, and then 4-20mA becomes 0-100 degrees.
Doing it this simplistically, though, reduces your resolution. I prefer to scale each input so that 4mA=4000 and 20mA=20000. Makes it easy to see the mA reading at a glance, and gives me plenty of resolution.
Then, you just use standard math to scale it accordingly. Most programmers who work with analogs frequently will build an add-on instruction to scale analog values, so that you just have to plug in the low and high analog values (4000 and 20000), and the low and high scaled values (0 degrees and 100 degrees) and the calculation is all done internally. But you can just as easily do it directly in ladder logic using a CPT instruction, or even a series of discrete multiply/divide/add/subtract instructions.
Plenty of ways to skin this cat, have a go and if you get stuck post back with where you're up to!