Would I still get a pass If I manage to get a merit or distinction on some of my unit

Hi,
I am a computer science student. I'm currently doing BTEC level 3 on college. On my course I've got overall 13 units which are spread on 2 years course. 7 units on the first year and the rest 8 units on the second year. My question is, If I get a pass on 4 of units and gets Merit or Distinction for the rest of the units, Would I get a pass or merit they calculate my overall grades?

There's not anywhere near enough information here to answer your question. You say, "If I get a pass on 4 of units" but don't give any clue as to which units these are. Your also say, "Merit or Distinction for the rest of the units". Merit and Distinction are very different results and have a very different overall impact.
Let me give you a brief overview of how your overall grade is determined to explain why the above is important. Every unit grade you get is converted into a number of points. The points you get depends on the grade, the size of the unit (some units are larger than others) and - for exams - your mark (not just your grade). They then total-up the points across all the units, and convert those overall points to an overall grade.
You say you're "a computer science student" and that "On my course I've got overall 13 units which are spread on 2 years". I'm going to assume this means you're doing a Pearson BTEC Level 3 National Extended Diploma in Computing, and use those units to illustrate the above. A pass in Unit 7 (IT Systems Security and Encryption) gets you 9 points, whilst a pass in Unit 10 (Human-computer Interaction) - if you took that unit - gets you just 6 points, because it's a smaller unit. A pass in Unit 1 (Principles of Computer Science) gets you anywhere between 12 and 19 points, depending on the mark you achieved (as it's a larger unit, and its assessed via an exam). So knowing that you got a pass in one unit just tells us you could have got 6 points or 19 points. That's quite a range and so can't be used to make any estimate as to your overall grade.
If you know which grades you've achieved in which units, then list them out below (e.g. Unit 1 = Pass, Unit 2 = Merit, etc.) - you can include estimated/predicted grades too if you like. We can then work out a likely overall grade. If you know you mark for any of the exams, that'd be even better.

My course - BTEC Pearson level 3 national diploma RQF (720) (2016 to present) in health and social care.

If I was to get a near pass or pass in my unit 4 exam what would my overall grade be considering:

Unit 1 (exam) -
My grade: pass
Size of unit: 90credits

Unit 2 (exam) -
My grade: merit
Size of unit: 120credits

Unit 4 (exam) -
My grade: pending
Size of unit: 120credits

Unit 5 (coursework) -
My grade: distinction
Size of unit: 90credits

Unit 7 (coursework) -
My grade: distinction
Size of unit: 90credits

Unit 8 (coursework) -
My grade: pending (predicted distinction) Size of unit: 90credits

Unit 10 (coursework) -
My grade: distinction
Size of unit: 60credits

Unit 11 (coursework) -
My grade: pending (predicted distinction)
Size of unit: 60credits

Unit 1 - a pass in a 90 GLH exam unit earns you between 9 and 14, depending on the actual mark you obtained in the exam.
Unit 2 - a merit in a 120 GLH exam unit earns you between 20 and 31 points, depending on the actual mark you obtained in the exam.
Unit 4 - a near pass in a 120 GLH exam unit earns you between 8 and 11 points, and a pass earns you between 12 and 19 points, depending on the actual mark you obtained in the exam.
Unit 5 - a distinction in a 90 GLH coursework unit earns you 24 points
Unit 7 - a distinction in a 90 GLH coursework unit earns you 24 points
Unit 8 - a distinction in a 90 GLH coursework unit earns you 24 points
Unit 10 - a distinction in a 60 GLH coursework unit earns you 16 points
Unit 11 - a distinction in a 60 GLH coursework unit earns you 16 points
So you have anything between 141 and 168 points. At 141 points you'd get a grade DM (for a DD you'd need 144 points). At 168 points you'd get a D*D (D*D needs at least 162 points). The most likely grade you'll achieve is a DD (which covers anything between 144 and 161 points).

How much would a merit get me in a 60 GLH coursework

How much would a merit get me in a 60 GLH coursework

And how much is a pass in 90GLH coursework