Newbie question on how to use pandas.rolling_mean

[zydjohn]

import pandas as pd

data = [1.0, 2.0, 3.0, 4.0]
s1 = pd.Series(data)
rollmean = pd.rolling_mean(s1, 2)
print(rollmean)

Hello, I changed my code according to your advice, but I got some warning:
Warning: pd.rolling_mean is deprecated for Series and will be removed in a future version, replace with
Series.rolling(window=2, center=False).mean()

However, I did see the result:
0 NaN
1 1.5
2 2.5
3 3.5
dtype: float64

I want to know how to use the new version or the version in future to do the same job.
Another issue is: the first value is: NaN
How I can either delete the first value or replace the value NaN by another value, i.e. 0.0
Thanks,