Level 4 is equivalent to roughly a first year university level Computer Science course in IT.
The BCS Certificate in IT has 3 parts, each with a corresponding exam (which must be passed to earn the certification).
Information Systems - which has 3 sections
Data Management
Systems Analysis and Design
Organisations
Software Development - which has 7 sections
Fundamental concepts of the programming process
Phase Specific Issues of Software Development
Introduction to Programming Concepts
Files
Intro to concept of user interface design
Role and need for system software
Case studies in problem solving/algorithm analysis
Computer and Network Technology - which has 4 sections
Fundamentals
Processor Architecture
Introduction to operating systems and system software
Networks
When preparing for these courses there is a wide range of free training and learning resources available for those wishing to study privately.
In order of increasing costs exam preparation approaches are
Self study using the recommended BCS books and various free self study course available via the internet, as well as Coursera and EdX courses (which are relatively inexpensive but provide little in the way of personal help and support)
A mixture of self-study and instructor / tutor based learning and progress coaching such as that provided by Croydon Tutorial College BCS HEQ Level 4 course modules.