An easy way to ensure your data is always up to date, whilst removing the need to manually select the refresh button is to setup a scheduled refresh.
Start by selecting your workspace
The main screen will show you 4 tabs. Select the 'Datasets' one.
Now select the 'Scheduled Refresh' icon against the dataset you want to have automatically refresh.
The 'Datasets' tab should already be selected, if not choose it from the top bar.
Now expand the 'Scheduled Refresh' section in the menu below by selecting the chevron.
This will reveal your options
Turn on 'Keep your data up to date' then select 'Add another time'
Now enter a time before you're first likely to view the report on a day (i.e. early morning). Remember, data is updated hourly, so add additional times if you'd like your data to be more up to date.
Select 'Apply' when done.
You'll get a message in the top right corner confirming if the schedule was applied successfully.
You're done, the data will now automatically refresh at your set time (providing your token hasn't expired, see below). If you selected the option to, you'll get an email should the refresh fail.
Use this feature in connection with the subscribe function (on the report) to get daily email updates of your data. (Subscribe is a Pro feature)
Alternatively, you can refresh the dataset at any time you'd like, by selecting the 'Refresh' icon on the dataset.
Refreshing (scheduled and otherwise) will only work for as long as your token is valid. Once expired you'll need to update the token for your report in PowerBI Desktop and re-publish to Service (You can simply replace your existing dataset and report))