How long have you had the bass? Is it new to you. If you've had it for a while is your high action issue new or has it always been high? If you sight down the neck, like aiming a rifle, can you see an upwards, string side, curve to the neck? If you fret your E string at the first fret and at the 20th, how much space do you have at the 9th fret between the string and fretboard. A "flat neck" normally will have a paper thin amount of space at the 9th fret when fretted at the fist and 20th.
Do you own a truss rod adjusting tool? It's a long neck 1/4 inch nut driver. If not you will need to obtain one in order to attempt to adjust your truss rods. If your neck is bowed then you will need to snug (tighten) the truss rod nuts in order to pull the neck back. Turn each nut no more than an eighth of a turn a day and give the neck a day to settle to the new strain. Never but put more torque on the nuts than you can exert with hand strength.
The reason for the "20 questions", I'd like to make sure you actually have a neck issue and not just a high bridge or neck set issue before monkeying with the rods. Truss rod adjustments are easy, it's just they are a bit daunting at first. It is necessary maintenance in reality unless you store the instrument in a climate/humidity controlled area where there is not change in either throughout the seasons.
Vintage/Classic Rickenbacker Enthusiast!
2011 4003 Jetglo
1986 4003 Shadow
2012 4004Cii TVY BH
1977 4002 Mapleglo
1982 4002 in Walnut