I've been playing the bass clarinet for almost two years now, and i cant get my tone on the upper register to sound nice though my tone is okay on the lower register. Also, i have spit issues. I tend to have a lot of spit and i cant last through a piece without having to stop playing and swallow my saliva.
Please help me, I really want to improve but i just dont know how..

Okay, I have been playing the Clarinet for 11 years, and the Bass Clarinet, the Contra-alto Clarinet, and even the Contra-bass Clarinet for 6 years, and I know what you are going through. For your tone quality on the upper register, a good instrument, a good mouthpiece, and a good ligature REALLY helps. Good Bass Clarinet brands are Buffet Crampon, Leblanc, and Selmer. The cheapest would be either Leblanc or Selmer. Good mouthpieces for Bass Clarinet are Clark W. Fobes' mouthpieces, the best Being the "Clark W Fobes San Francisco Bass Clarinet Mouthpiece", and Selmer mouthpieces, the best being the "Selmer C85 Bass Clarinet Mouthpiece". Personally, I use the "Clark W Fobes San Francisco Bass Clarinet Mouthpiece", although those those mouthpieces are a bit pricey. When it comes to ligatures, try to use a non-metal ligature, but if you squeak a lot, metal ligatures help with that. Good non-metal ligatures are BG, and Rovner. I use (and love) the "BG Super Revelation Bass Clarinet Ligature", but Rovner is really good too. Good brands for metal ligatures are Vandoren, the best being the "Vandoren M/O Bass Clarinet ligatures", "BG Tradition Bass Clarinet Ligature". Also, make sure your reed and ligature placement is correct, check with a teacher or preferably a professional clarinetist. Also, good embouchure is key, and whatever you do DO NOT BITE, if you are able, try to play double-lip embouchure, which is when you cover your top teeth with your upper lip like you are playing on an oboe type reed, and, instead of biting to get control, you use your lip to increase friction on the reed to gain control. Part of double-lip is to use friction instead of force on the reed, in order to do that, keep your bottom lip rolled under the reed (at this point, keep the mouthpiece barely in your mouth), and push the mouthpiece farther in your mouth, as you put the mouthpiece farther in, do not move your lip, but let more of your lip touch the reed. This takes a lot of time and practice to master. This is also a good thing to apply to all clarinets. As for spit, make sure to have a good and tight embouchure, and NEVER puff your cheeks out, make sure they are close, make sure your tounge is up and not low, because when your tounge is lower, that stimulates your saliva glands to produce more, so that is bad, as you know. If you can, keep a small cup or container of some sort near you, so if you do build up saliva, you can quick spit it out in the cup.

I hope I have helped you.

Good luck!

Well, if you want to decrease your spit (saliva) then you can start with the foods you eat. Eat more green vegetables. Eat less acidic foods such as meat, dairy , sugar, and refined grains. Staying healthy can improve your playing ability and have more fun.