Hi Loren,
I guess there is no trick, because I suppose no older NET Framework version can be installed if a newer is presented already. You can try to unistall existing one (I guess it's 4.6.x) or even more of them and try the installation again. But this process can be painful if something is broken. There are advices from Microsoft how to troubleshoot NET Framework (un)installation.
In fact 4.6.x should be enough to run applications targeting 4.5.x, because higher versions are "highly compatible" (quoted from Microsoft information ;-), but it seems it does not happen in your case.
You can also try to .NET Framework Setup Verification Tool, maybe this tool will find what is wrong. Links to repair tools are mentioned in the article also.
I am not sure, but another way maybe to install multitargeting pack, which are normally installed as a part of Visual Studios and NET SDKs.
With regards,
Jan