yes. you can restore defaults in the launcher. which will let you access manage user file in the sim and you can delete it there.
restoring defaults also wipes you pilot profile settings and recent flight history does not damage/remove any planes
OR you can delete the model from the rf directory in windows explorer. in documents/realflight G5/Vehichles/CustomModels (delete the folder and the .bse file) and in documents/realflight G5/Vehichles/CustomVehichles delete the .RFVehichle