Go to file catalog/view/YOUR-THEME/default/template/account/register.php,
Search for the line :
<input type=”password” name=”password” value=”{{ password }}” placeholder=”{{ entry_password }}” id=”input-password” class=”form-control” />
Replace It with :
<input type=”password” name=”password” value=”{{ password }}” placeholder=”{{ entry_password }}” id=”input-password” class=”form-control” pattern=”^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[$@$!%*?&])[A-Za-z\d$@$!%*?&]{8,}” title=”Minimum eight characters, at least one uppercase letter, one lowercase letter, one number and one special character” />
