To change your avatar gender, click on the Outfit Window at the bottom of the screen. When the outfit window opens, click on the 'New' outfit button.
After you click on 'New', you will see two boxes, one with 'Enter Name' and one with 'Base Male'. The enter name box is to enter the name of the outfit you want to create. The Base Male drop-down menu with give you the option of Base Male or Base Female. Choose which gender you want your avatar to be with these. When you are done with naming the outfit and changing the gender, click on the 'Create' button to create the outfit with the gender you picked. Give it a a couple of seconds to change.
From there you can Save and Close the outfit window.
To change genders in your profile, click on the three dash menu button in the top right hand corner of the screen. When the menu opens, click on 'Edit Profile'.
When the profile is open, click on 'More'.
This will open a full profile. At the bottom of this, there is an 'Edit' button.
This will be the next display you see after clicking Edit.
Here you can change your name, and add other information about you. To change the gender in your profile, click either the male or female check boxes.
Save the edit afterwards, and the gender will be saved.