Solenoid design

[gm123456@xxxxxxxxx]

Hello,

I am a beginner in the world of magnetics and I am trying to juice up 
a solenoid. The maximum force the solenoid has is about 45 gf. I need 
about 90 gf. Furthermore, I have to try to reduce the heating up of 
the solenoid. The outer dimensions of the solenoid can not be 
changed. How can I improve this solenoid? More, thicker windings? 
Different materials?

Thanks in advance for all your time and effort,

Gert