Your motor has 3 latches, aft and both sides. The levers have to be pulled outward then rotated to unlatch the cover.
It the motor was used in saltwater and the cover not removed for over a year, the latches may be tight. Newer models have grease nipples on the linkage. If your have an earlier 115, then you may have to disassemble the latch and grease with Evinrude Triple Guard after cleaning out any corrosion.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.