How to mesh 3D SOLID

How do I change 3D SHELL ELEMENTS into 3D SOLID ELEMENTS? And how to remove 3D TRIANGULAR SHELL ELEMENTS? I am complete beginner. Please teach me to mesh properly. Thank you.

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** Altair Radioss(TM) Starter 2019.1 **
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** Non-linear Finite Element Analysis Software **
** from Altair Engineering, Inc. **
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** Windows 64 bits, Intel compiler **
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** Build tag: 0972239_1285320191_1020_0062808_10 **
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** COPYRIGHT (C) 1986-2019 Altair Engineering, Inc. **
** All Rights Reserved. Copyright notice does not imply publication. **
** Contains trade secrets of Altair Engineering Inc. **
** Decompilation or disassembly of this software strictly prohibited. **
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.. BLOCK FREE FORMAT

.. STARTER RUNNING ON 22 THREADS
.. CONTROL VARIABLES
.. UNITS SYSTEM
.. FUNCTIONS & TABLES
.. MATERIALS
.. NODES
.. PROPERTIES
.. 3D SHELL ELEMENTS <<<<<<<<<<<<<<<<<<<
.. 3D TRIANGULAR SHELL ELEMENTS  <<<<<<<<<<
.. SUBSETS
.. ELEMENT GROUPS
.. PART GROUPS
.. SURFACES
.. NODE GROUP
.. BOUNDARY CONDITIONS
.. IMPOSED VELOCITIES
.. INITIAL VELOCITIES
.. DOMAIN DECOMPOSITION
** ERROR TRAPPED : REPORT TO LISTING FILE
ERROR ID : 760
RADIOSS STOP DUE TO INPUT ERROR

==== End of solver screen output ====

==== RADIOSS Job completed ====