Hello Alan
Say Q2 is the BJT you want to vary the temperature.
Define a parameter TempQ2
Ctrl-Right clic on Q2 symbol
Enter temp={tempQ2} on the line2
In your schematic enter
.step param tempQ2 list 0 25 50
or
.param tempQ2= 13
See the Help with keywords Q. Bipolar Transistor
Regards
PhB