Since I just started getting familiar with forecasting, so I stumbled upon the example

To forecast 5 years you can use h to set the number of forecasts:

autoplot(lungDeaths)   
  geom_forecast(h = 60, showgap = FALSE)

Output:

To remove the confidence intervals use PI:

If FALSE, confidence intervals will not be plotted, giving only the forecast line.

library(forecast)
autoplot(lungDeaths)   
  geom_forecast(h = 60, showgap = FALSE, PI = FALSE)

Output: