You can't and you don't really need to because there is no level cap so you'll eventually fill up everything you want.
You can alter in via the console ( pre ~ to bring up that).
- Type 'Player.modav <attribute> <value>' to mod attributes.
- Prefix the <value> with a '-' sign to *reduce* the attributes magnitude. IE, -5 to reduce an attribute by 5 points.
- Type 'Player.RemovePerk <perk code>' to remove perks.
- Type 'Player.AddPerk <perk code>' to add perks to replace the ones you removed.
Here's a list of the perk ID numbers <perkcode>.
Or can download a mod that allows you to reset them all.