how to reduce file size

hi all,

I have file size of 30mb assembly file... i convert this assembly to part model.. then the file size increase 35 mb... again i open new assembly file and added the part file into assembly... now the file size comes around 5 mb... but the problem is some of the parts file is missing in the assembly..                   

Did anybody know the solution for this or anyother solution to reduce the file size

SolidworksGeneral