The last stable release of 5.1 was 5.1.3 which was released on 14 March 2013. The first release where you were able to disable TLS 1.0 and enable TLS 1.1/1.2 is 5.3.6 which was released three years later on 1 March 2016. Even if you could get to View 5.3.6 the versions of vSphere/ESXi that you are running will still require TLS 1.0. Due to the age of this environment and the fact that it's no longer supported I would not advise an upgrade. You should prioritize moving off of this environment ASAP.
VMware Horizon View 5.3.6 Release Notes
As with previous View 5.3.x releases, TLS 1.0 is enabled by default on View servers and the View Composer server. TLS 1.0 is considered insufficiently secure and US-CERT alert TA15-120A recommends disabling TLS 1.0. For View servers, you can configure the security protocols by following the instructions in Configuring Global Acceptance and Proposal Policies in the View Security document. For instructions on how to configure security protocols on the View Composer server, see Microsoft article https://technet.microsoft.com/en-us/library/dn786418.aspx. Note that the versions of vSphere that this View release supports must be patched to enable TLSv1.1/TLSv1.2. If you disable TLS 1.0 on View Composer server or View Connection Server without patching vSphere, View will not be able to communicate with vCenter Server.
Status of TLSv1.1/1.2 Enablement and TLSv1.0 Disablement across VMware products (2145796)