Student or Learner
"Had better" refers to the immediate future. It is more urgent than "should" or "ought to." Compare:
I really ought to go and see Fred one of these days. ~ Well, you'd better do it soon -- he's leaving for South Africa at the end of the month."
The source: Practical English Usage (p. 203)
I'd like to ask what if I use 'should")' instead of 'had better'. I mean, how it changes the meaning?
Yes, you can use "should" there and I can see no difference in meaning.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.