I have to review the bank's budget for the upcoming year, and I don't know how to proceed.
Can you help me?
What are the steps to perform this assignement?
Thanks in advance

Review for what exactly?

Review the budget to see if it is correctly prepared:
I have to focus on the assumptions:
Are they correct?
Do they reflect the reality?
Are there some threads that were omitted?

Wow - that is quite an assignment for one person if you are talking about the budget for the entire bank. I would assume that each individual area of the bank is required to submit their budget for the year along with sufficient justification documentation. I guess you would have to review all the justification documentation for reasonableness, check the budget numbers for accuracy compared to their justification documentation. etc. Other than that, I would be at a loss how one person could be enough of an expert in every aspect of the bank to do much more.

Since The bank I work for is a small one I think I will be able to do it and further correction to my work will be done in the upcoming budget reviews next years