iphone 4s keeps freezing and apps keep crashing

so it basically says it all up in the title, but my phone keeps freezing and whenever i open apps they freeze and then crash!

i dont know if i should get a new phone like get it replaced or if i shoud reset it, or just try and get it fixed, someone help!!

thanks! also, whether im connected to wifi or not, my phone is always so slow!! i dont have like any music or photos on it cause i thought that would make it work and it hasnt! i really dont wanna have to reset it!

please help!!