Clutch problem

I have a 1998 Nissan Altima, manual transmission. It has about 104K miles. Recently I started having problem with the clutch. When I press the clutch to switch gears, specially from 1st to 2nd and 2nd to 3rd, the tach does not drop all the way to 700rpm. Sometimes the tach drops a little and sometimes it just stays put when I change gears. Also sometimes when I press the clutch (to change gears) the rmp goes up. Does anybody know why this is happening? Do I need to change transmission fluid or I have something more serious? Any help is appreciated. Thanks