Note beams are set automatically, based on the time signature. To adjust the default beaming, right-click on a time signature and select "Time Signature Properties." See Change default beaming for details.
However, if you want to adjust note beaming manually, on a case-by-case basis, use the beam symbols found in the Beam Properties palette in the "Basic" or "Advanced" workspaces:
The following is a list of beam symbols and their effects:
To change one or more note beams (except feathered beams, below), use either of the following methods:
Drag and drop a beam symbol from a workspace onto a note in the score.
To apply feathered note beams, use either of the following methods:
Drag and drop a feathered-beam symbol from a workspace onto a note beam in the score.
Select one or more note beams in the score, then double click on a feathered-beam symbol in the workspace.
Notes: (1) Feathered beams may use 2 or 3 lines depending on the tempo and the desired rate of the change; (2) To create a 2-line feathered beam, you need to start with a continuous run of beamed sixteenth notes; (3) To create a 3-line feathered beam, you need to start with continuous run of beamed thirty-second notes; (4) Playback of feathered beams is not supported.
Alternatively, you can use the Inspector for all of these operations:
If you want all note beams in the score to be horizontal there is a "Flatten all beams" option in Style→General→Beams.
To adjust feathered beams:
MuseScore (following accepted music engraving practice) spaces notes according to their time values, allowing for accidentals, lyrics etc. In systems where there is more than one staff, this may result in irregular note spacing, as in the following example:
Local relayout is a tickbox option in the Inspector allowing you to specify those passages in the score where you want the note spacing to be independent of other staves in the system. Applying "Local relayout" to the note beams in the top staff of the previous example results in a more even distribution of notes:
To do a local relayout:
To flip a beam from above to below the notes, or vice-versa:
To restore beams to the mode defined in the local time signatures: