Hello, i have a 1995 volvo 850 wagon. The other day i was driving and it just stopped going, it is an automatic. it will not go in reverse and when i put it in drive it just revs up? Should i change the fluid?

no, a fluid change will not cure this, if very low on fluid, yes that may be,

Unfortunately you're way past a fluid&filter change! Volvo's are very high maintenance vehicles. In your situation what has happened here is that your transmission fluid was either so low for so long or low & burnt out,(extremely old) that 1 of 2 things or both occurred! The clutch packs and or the front pump on the transmission are no good! Comman problem on Volvo's! In any event your transmission is burnt out&they are expensive! Your best bet is to finding a dependable parts dealer who deals in used vehicle parts! Good luck (keep up on the maintenance its cheaper than buying new parts!