1. Hold down CMD + Space to bring up the Spotlight Search
2. Type in System Preferences so that you can open your System Preferences,
3. Select System Preferences in order to open it, it should look something like this
4. Select Users and Groups (you can see it in the bottom left in the screencap above)
This will take you to your account page.
It should look something like this:
You can see that my account is an admin because it has the word "Admin" under it,
If you do not see the word admin under your account name then you are not an admin.