After passing the tutorial level, "Carriage House", you will be prompted to enter your name. Enter Rosmarus and select "OK". If you were already past the tutorial, scroll from the map screen to the "Settings" menu by selecting the bottom-left icon at the "Weather" menu. Select "Save Sessions" and choose your current session. Your stats for the saved game and your name at the top will appear. Select your name and change it to Rosmarus. Next, enter the "Spider Types" section of the menu by selecting the bottom-left corner icon until it appears. This screen contains the different spider types you can play as. They will all now be unlocked. Select the last one, "O. Walrus", to view its image and assign it to be as your in-game avatar to play as a walrus. You can then change your saved game name back to whatever desired.