According to CSF security check, I need to upgrade Apache version2.0 and Mysql version4, I am using a Centos5 / WHM , here is what I need to know:
1- would upgrading Apache cause any problems?
2- would upgrading mysql from version 4 to 5 make some DB’s to go down?
3-In case i get problems with mysql, how to go back to version 4?

Thank you in advance.