Sahil Sura
Ansys Employee

Hi chiheb ben abdallah,
If the computational limitation is present, you can go for Linear elements (single order), as the default mesh uses second-order elements. This will help you see a change in the solution time as a relatively less number of equations will be formed for the solver to compute.
Mesh (
You can also go for mesh sizing options, to mesh the critical areas with relatively fine mesh.
Specifying an Appropriate Element Size for Stress Analysis — Lesson 1 - ANSYS Innovation Courses
You can also try solving the model using symmetry if the boundary conditions suit for the some cases.
Understanding when to Take Advantage of Symmetry - Lesson 3 - ANSYS Innovation Courses

Also, you can find the latest version of Ansys Student from the following link- Ansys Student Versions | Free Student Software Downloads
Hope this helps!