Intelligence is governing: Enchant / Conjuration / Alchemy / Security.
To have 5 points to level Intelligence you must have 10 points.
Either 10 points in Enchant, or 10 in Conjuration, or 10 in Alchemy, or 10 in Security.
OR:
Some points in Enchant, some points in Conjuration, some other points in Alchemy and others in Security: For a total of 10 points...
Those 10 points of skills governed by Intelligence will give the 5 points you need to level up in a correct way.
If you have in your major or minor skills a skill governed by Intelligence, be careful not to increase too quickly.
Let's say you have Enchant in your major skills, Conjuration in your minor skill and Alchemy in your misc. skills, be aware not to increase Enchant or Conjuration if you have already increased 10 points in Alchemy. You'll need to increase other skills in misc skills (like short blade for Speed) and then you can increase a major or minor skill governed by another attribute like Strength. I really hope I made it clear...