Before anything else, PUT NEW STRINGS ON. Fixing a tone issue doesn't work with dead, old, groaty strings.

1: play with the EQ on the amp. try turning the bass down if you have a bass-heavy neck pickup.

2: If that doesn't work, try moving the bass side of the neck pickup down, away from the strings. You do this by loosening the adjustment screw on the bass side of the pickup

NOTE: The general rule for pickup height is a little over 3mm on the bass side, and about 2.5mm on the treble side. I measure by placing metric allen wrenches on the pickups. I use a 3mm on the bass side, bring the pickup up until the allen wrench just touches the string, then back it down a hair. I do the same thing on the treble side with a 2mm allen wrench.

3: If that doesn't work, open up the electronics and check your pot values. If it's a humbucker, general rules say it should have 500k pots. Single coils "should" use 250k pots. Just look on the bottom or side of the pots.

If none of that works, take it to a competent tech.