Play a tremolo from piano to forte

[Peter van Dijk]

This is my second message on the forum.
I'm 41 and started to play the piano two years ago.
Once every two weeks I have a lesson of one hour.

How do I play a tremolo (over an octave) from piano to forte.
Do I keep my fingers on the keys or do I lift them to play forte ?

Is there an exercise to practice a tremolo ?
I can only play 4 notes at an even tempo, than I loose speed.

[BoliverAllmon]

This is my second message on the forum.
I'm 41 and started to play the piano two years ago.
Once every two weeks I have a lesson of one hour.

How do I play a tremolo (over an octave) from piano to forte.
Do I keep my fingers on the keys or do I lift them to play forte ?

Is there an exercise to practice a tremolo ?
I can only play 4 notes at an even tempo, than I loose speed.

the perfect exercise is to just tremolo more.